Gemstone Varieties
As with many of the vague terms used to describe the various microcrystalline quartz forms, the exact definition of “agate” has never been officially determined. However, most agates include more than one color and the various sub-variety names often describe what the resulting color patterns most closely resemble (e.g., fortification agate, lace agate, tube agate, dendritic agate, banded agate, etc.).
While much of the above could also be equally applicable to jaspers, it is the stone’s translucency, or a lack thereof, that differentiates these two chalcedony groups, with most varieties of agate possessing some degree of translucency. This distinction can be most clearly seen when comparing the visual appearances of translucent moss agate and the similarly named, opaque moss jasper.
The distinctive wavy parallel banding seen within banded agate make it perhaps the best-known sub-variety, with thin slices of the material being a staple of many gift shops.
A member of the feldspar family of minerals, amazonite is the name given to gem-quality green to greenish-blue microcline with distinctive white streaks. Usually lacking the transparency and crystal size ideally required for faceting, most material is fashioned into cabochons, carvings, beads or irregular tumbled forms. However, a small number of crystals from Myanmar’s famous Mogok gemstone tract have been faceted.
Also sometimes known as Amazon Stone, the mineral is named after a historical deposit located close to the Amazon River, but it is now believed that this green material was actually nephrite jade. While sources for genuine amazonite have since been found within Brazil, they are all located far from the river from which the mineral takes its name. Amazonite is also found in Russia, Madagascar, Ethiopia and the American state of Colorado, with the latter giving rise to the misnomer “Colorado jade”.
Visual Observations: Luster: greasy - dull, engine - turned effect
Hardness: 2 - 2.5
Treatments: Irradiation, Heat treatment, Dyed
Amber is an example of an organic gemstone, due to it having been formed from fossilized pine tree resin that hardened over the course of tens of millions of years via a process known as polymerization. However, as this substance was initially somewhat soft and sticky, ambers sometimes contain well-preserved animal and/or plant material that became trapped within the fluid prior to its solidification.
Amber's use within items of decoration and personal adornment can be provably traced back over 10,000 years to the Neolithic period, thus making it one of the earliest-known gemstones. The ancient Greek philosopher Thales of Miletus discovered that amber, known at the time as “elektron”, possessed the ability to attract objects towards it after being rubbed. As a result, when a concept was developed to explain this phenomenon over two thousand years later, it was named electricity in reference to the material. Learn more
Amethyst is a variety of quartz, which is defined by its purple or violet hue. This coloration results from the presence of ferric iron within the quartz structure.
The name is derived from the Greek words for "not drunken", as it was once believed that the stone could help prevent intoxication from alcohol consumption. Throughout the classical and medieval periods, the value of amethyst was actually far higher than it was today. The high price of dyes had made purple the color of emperors and kings, and the stone itself was extremely scarce. However, the subsequent discovery of an almost unlimited supply in South America pushed amethyst prices to the other extreme, and the gem is now one of the most commonly encountered and inexpensive within the marketplace.
Visual Observations: Often used as doublet, triplet. It's a fossilized shell of an extinct nautilus-like animal, may be spiral, mosaic patterns.
Hardness: 4
Treatments: None
Ammolite is an opal-like organic gemstone found primarily along the eastern slopes of the Rocky Mountains of North America. It is made of the fossilized shells of ammonites, which in turn are composed primarily of aragonite, the same mineral contained in nacre, with a microstructure inherited from the shell.
Anatase
Along with the more common rutile and brookite, anatase is one of the three forms of titanium dioxide. The mineral is usually only sold in its natural form to collectors, but faceted stones are very occasionally also encountered in sizes below one carat. While most crystals are actually brownish or blue, the majority are sufficiently dark in tone so as to appear almost black.
The mineral was named in 1801 after the Greek word for “extension”, as its crystals are longer than those associated with its polymorph, rutile. The two minerals can also be differentiated by anatase’s lower measurable hardness (5.5-6.0) and density, as well as its distinctive sub-metallic luster. However, when heated to temperatures in excess of 915 degrees Celsius, anatase transforms into the more stable rutile.
Andalusite (Chiastolite)
Alongside kyanite and sillimanite, andalusite is one of the three aluminosilicates that may occasionally be encountered as gemstones. The crystals possess perhaps the strongest pleochroism in the gem world, with the cutting orientation and/or viewing direction giving rise to either a brownish-red, brownish-yellow or greenish hue.
Andalusite takes its name from the southern Spanish region of Andalusia, where it was first discovered. However, Brazil is now the primary producer of gem-quality material, with significant deposits also found in Sri Lanka, Russia and the United States.
Viridine is a manganese-containing subs-species of andalusite, which is noted for its bright yellowish-green coloration. Another variety, known as chiastolite, possesses a distinctive dark cross of graphite against a light gray background, and is of great interest to both mineral collectors and Christians alike.
Visual Observations: Often imitate Paraiba tourmaline
Hardness: 5
Treatments: Heat treatment
Apatite is the most abundant phosphate on earth and is the material that makes up our bones and teeth. It is also the main source of elemental phosphorus required by the plant kingdom, as well as for the production of toothpastes, fertilizers, fireworks, detergents and pesticides. Furthermore, despite its relatively low hardness (5.0), large apatite crystals are also occasionally fashioned into both faceted and cabochon-cut chatoyant gemstones, with the latter’s optical effect caused by the presence of fine, needle-like rutile inclusions within a stone.
Due to the fact that its crystals are found in almost every basic hue, apatite is able to mimic many other, often more valuable, gem varieties such as Paraiba tourmaline. In fact, the name is derived from the Greek word meaning “deceit” for this very reason.
Formula: Ca5(PO)3(F,OH,Cl)3
Crystallography: Hexagonal, Crystal usually promatic or stubby
With a name derived from the Latin for “sea water”, aquamarine is a well-known variety of beryl that owes its light blue coloration to the presence of ferrous iron within its internal crystal structure. However, as beryl's yellow-producing chromophore (i.e., ferric iron) is usually also present, most material initially tends to be somewhat greenish and is routinely subjected to heat-based treatments in order to produce more saleable pure blue hues. Aside from their distinctive color, aquamarine crystals are also noted for their large sizes and typically very high levels of clarity.
While Brazil is the world’s primary source for gem-quality aquamarine, commercially significant deposits are also located within Mozambique, Nigeria, Zambia, Madagascar, Pakistan and Vietnam. In addition, Brazil and Mozambique produce a very intensely colored sub-variety known as “Santa Maria”, which was named after the former’s Santa Maria de Itabira mine from where it was first discovered.
Visual Observations: Ex doubling in single crystal
Hardness: 3
Treatments: Dyed
Calcite is an abundant calcium-containing carbonate, which is noted within industry as an important ore for the metal and as a key ingredient within important household chemicals such as paints and fertilizers. Due to its extreme softness (3.0) and, like all carbonates, vulnerability to attack from even the weakest of acids, the mineral lacks the durability usually required for jewelry wear and is instead usually encountered as a collectors’ mineral. In addition, calcite comprises the often unwanted, whitish regions within lapis lazuli.
Aside from its very occasional use as a gemstone, calcite is perhaps best known to gemologists as the key optical component within many gemological dichroscopes. These devices make use of the mineral’s inherent ability to split incident light into its two constituent rays, and these are subsequently able to individually display the two or three hues that emanate from the pleochroic gem material under test.
Cassiterite, nicknamed "the tin stone”, is a fairly common oxide, which is noted for historically being the most important ore for the extraction of tin. In fact, the mineral’s name is actually derived from a Greek word for the metal, kassiteros. Tin was especially important in the ancient world, as it is used in combination with copper to produce bronze.
Due to its very high physical (SG = 6.7-7.1) and optical (RI = 2.0-2.1) density, cassiterite is able to display flashes of spectral “fire” to an even greater extent than diamond. In addition, the polished material possesses a diamond-like adamantine luster. However, while cassiterite can occur in a wide range of hues, gem-quality reddish, greenish, brownish and/or yellowish crystals tend to be far rarer than the less desirable, overly dark material.
Chrysoberyl (All varieties)
Visual Observations: Alexandrite (color-change) often strong pleochroism, good quality cat's eye may have "milk & honey", "open & closed eye" effect.
Hardness: 8.5
Treatments: Irradiation
While non-phenomenal yellowish, greenish and/or brownish chrysoberyl is encountered within the marketplace as a faceted gemstone, the species is best known for its chatoyant and color-change varieties.
Chatoyant chrysoberyl is prized for its ability to display a very sharp optical effect without sacrificing other visual factors such as translucency, clarity and body color. As a result, the unqualified term “cat’s eye” is generally reserved for chrysoberyl specimens, with other chatoyant gem varieties prefixed with the name of the mineral species to which they belong (e.g. cat’s eye tourmaline, etc.).
Alexandrite is the color-change variety of chrysoberyl, and, like cat’s eye, it is the most desirable and valuable gemstone of its kind. Named in honor of the future Tsar Alexander II, who came of age around the time of its 1834 discovery in Russia’s Ural Mountains, the finest alexandrites are raspberry-red under indoor incandescent lighting and emerald-green in sunlight.
Chrysocolla
Visual Observations: Look like turquoise.
Hardness: 2 - 4
Treatments: None
A copper-containing silicate of variable, and often uncertain, composition, chrysocolla has been used as an ornamental material since the antiquity. The cyan-colored mineral is often found in close association with its better-known copper-containing counterparts, namely azurite, turquoise and malachite, with these four materials together comprising the green and blue “Eilat stone” of ancient Israel. When intergrown with the much harder quartz, chrysocolla forms a significantly more durable, rare and valuable gemstone known as “chrysocolla chalcedony” or “gem silica”.
Chrysocolla is usually encountered in the form of veins, crusts and botryoidal, or “grape-like”, masses within the exposed oxidation zones of copper deposits. The most significant of these are located within Israel, DR Congo (Zaire), Chile, Mexico, Russia, Peru and the United States (Arizona), with the latter two localities also producing the valuable, quartz-containing material described above.
Chrysoprase is a well-known variety of massive quartz (i.e. chalcedony), which has been colored yellowish green to bluish green by the presence of nickel impurities within its crystal structure. As one of many gem materials prefixed by the Greek word for “golden”, chryso, chrysoprase hues are usually lighter in tone and brighter than those of its deep green counterpart, prase. However, the transitional point between these two chalcedony varieties has never been officially determined, and borderline cases are likely to be sold as the more valuable chrysoprase.
Today, around 85% of chrysoprase is mined in Australia, so when the material is employed to simulate jade it is usually sold under the misnomers “Australian jade” or “Queensland jade”. However, these two completely unrelated gem species can be easily differentiated by way of chrysoprase’s greater degree of translucency and lower density.
Citrine is a variety of macrocrystalline quartz, which is defined by its somewhat yellowish hues that result from the presence of ferrous iron within the quartz structure. Chemically-speaking, citrine only differs from amethyst by way of its iron oxidation level, and can therefore be produced by heating its purple counterpart. As amethyst tends to be more commonly encountered in nature, most citrine in the marketplace is actually “burnt amethyst”.
While its varietal name is derived from the French for "lemon", citron, citrine is not to be confused with what we refer to by the trade-name of “lemon quartz”. This lesser-known gem variety differs from citrine by way of its pure yellow or slightly greenish hues, which contrast with citrine’s more orangish yellows. In addition, the coloration of lemon quartz is always produced artificially via irradiation and subsequent heating, while citrine is only merely heated in the way described above.
Visual Observations: Often light in tone and fluoresces light blue, confused with topaz and apatite.
Hardness: 7
Treatments: None
Danburite is a silicate of calcium and boron, which is occasionally encountered as a faceted gemstone. The mineral is reasonably durable, due to its relatively high hardness (7.0-7.5) and lack of vulnerable directional cleavages. In addition, crystals can be found in sufficiently large sizes for faceting into stones of up to five carats. However, danburite’s popularity as a gemstone has been held back by its limited name recognition amongst the jewelry-buying public and the lack of a constant and reliable supply of facetable material.
Named in 1839 after its original source locality of Danbury, Connecticut, most danburite gemstones encountered within the marketplace have been faceted from colorless to pale pink Mexican crystals. However, Myanmar's famous Mogok gemstone tract is an important source for the preferred yellowish and/or brownish material, with these stones becoming rarer and more valuable as their hue saturation increases.
Visual Observations: Sharp facet junctions, naturals with trigons, bearding , waxy to granular girdle surface no see-thru.
Hardness: 10
Treatments: Fracture filling, HPHT, Laser drilling, Irradiation
Diamond is unique within the gem world as it is fundamentally composed of only one type of atom, namely carbon, and is therefore an element rather than a compound. If a diamond’s basic crystal structure has not been altered and no trace impurities are present, the stone will be colorless.
Diamond’s name is derived from the Greek word meaning “unconquerable”, as the crystals’ inherent high hardness made them difficult to cut and polish. This is one of the reasons why its status as the world’s best-known gemstone is actually a relatively recent phenomenon.
Another issue prior to the 18th and 19th century Brazilian and South African discoveries was the limited supply, with India having previously been the only noteworthy locality. Today, diamond extraction is primarily associated with Africa, but Russia, Australia and Canada are also important sources for gem-quality material outside De Beers’ sphere of influence.
Diaspore
Diaspore is an aluminum oxide hydroxide, which is noted within the gem trade for its color-change variety.
First discovered in Russia’s Ural Mountains 1801, the mineral is named after the Greek for “to scatter” as it was known to break apart when exposed to high temperatures. However, for more than two centuries it was of little gemological interest, due to its pale hues and cutting complications arising from a perfect cleavage. However, the 2006 discovery of Turkish color-change material suddenly brought diaspore into the spotlight.
Known by a variety of unofficial marketing names, including zultanite, csarite and ottomanite - as well as the misnomer “Turkish alexandrite” - these stones display a light yellowish green in daylight and a pale pinkish orange when illuminated by indoor incandescent light sources.
Visual Observations: star often 4- rayed
Hardness: 5.5 - 6.5
Treatments: None
Despite having been first identified at the turn of the nineteenth century, diopside’s relatively low hardness (5.5) and dull range of colors prevented it from having any significant gemological impact until the discovery of bright green Siberian material in 1988. Although still soft, these "chrome diopside" crystals possess a hue that rivals that seen in the far more expensive tsavorite garnet, as well as the finest emeralds and jadeite.
While the next best-known variety, star diopside, displays a sharp four-rayed asterism effect, the stones lack popularity due to their somewhat blackish coloration and opacity. Conversely, the less well-known cat’s eye specimens usually display attractive green hues and possess far higher levels of translucency.
Yellowish-green faceted diopside has recently been sold under the trade name of "tashmarine", while violane is a light bluish and/or violetish microcrystalline variety that is usually fashioned into cabochons, beads and polished irregular forms.
Visual Observations: Dark color or high saturation. Commonly twin crystals, color is similar to fine emerald but slightly more blue.
Hardness: 5
Treatment: None
Dioptase is a copper-containing silicate, which is noted for its highly saturated green to bluish-green hues. While the mineral is very popular with mineral collectors, a relatively low hardness (5.0) and scarcity of large, clean crystals have limited its appeal as a gemstone.
When a large number of green crystals were first discovered within modern-day Kazakhstan at the end of the eighteenth century, it was initially believed that a new emerald deposit had been discovered. However, subsequent analysis in Moscow determined that the hardness of the crystals was far below that of beryl, and they were deemed to be a previously undiscovered mineral species. It was subsequently named dioptase in reference to its two highly visible cleavage directions, and additional sources have since been discovered in Namibia and the Republic of Congo.
Emerald is a variety of beryl, which is defined by its green color. This coloration results from the presence of chromium and/or vanadium within the beryl structure, and beryl's colored green by iron are instead simply known as "green beryl". In addition, the necessity for emeralds to be green means that the terms "pink emerald" (i.e., morganite) and "red beryl" (i.e., bixbite) are misnomers.
The current name is derived from the ancient Greek words for "green gem", but the gem had been mined in Egypt since around 1500 BC. However, the discoveries of emeralds at Muzo and Chivor, in modern-day Colombia, were the most significant in terms of both the quality and quantity of material available to the market.
Emeralds are often of low clarity, and the visibility of the internal fractures is often decreased with the addition of resin-based filling substances.
Enstatite is magnesium-containing silicate, which is found in a variety of brownish, greenish and/or yellowish hues. Due to the mineral's relatively low hardness and the rarity of facetable transparent raw material, it is generally regarded as being a more of a collector's stone than something you are likely to find in the mass market.
However, an opaque brown variety called bronzite is commonly fashioned into beads and carvings, as well as often being encountered in irregular tumbled forms within necklaces and bracelets. This material has a very distinctive appearance, with fine films of separated iron oxide displaying a somewhat reflective sub-metallic luster.
In addition, the presence of fine needle-like inclusions within some enstatite crystals will cause a well-defined cat's eye effect to be displayed when the stone is cut en cabochon.
Visual Observations: Often dark tone strong pleo and may show pseudo-uniaxial optic figure.
Hardness: 6 - 7
Treatments: None
Epidote is the name given to a group of complex silicates, but also denotes the most common individual member within this group. The mineral is almost always greenish in color but ranges from a fairly light yellowish green to a dark green that verges on black. However, of most interest to collectors is the medium-toned pistachio green material, which is sometimes known as pistacite.
Epidote was named in 1801 from the Greek meaning “increase”, as one side of the prismatic crystals is longer than the other. These crystals tend to be well-formed and can be found in some interesting groupings, thus making them popular with mineral collectors. As a result, very few transparent epidote crystals are sacrificed for faceting.
Unakite is a green and pink rock that contains a mixture of epidote, orthoclase feldspar and quartz. It is usually tumbled, fashioned into cabochons or used for carvings.
The feldspars are a large group of aluminum-containing, monoclinic or triclinic silicates that comprise the majority of the earth’s crust. They are classified by way of the relative quantities of potassium, calcium and/or sodium that are present within their respective compositions, with the primary divide occurring between the calcium-containing plagioclase feldspars (i.e., anorthite, bytownite, labradorite, andesine and oligoclase) and the potassium-containing alkali or k-feldspars (orthoclase, sanidine and anorthoclase). However, albite - which is the sodium-dominant member of the group - also possesses small amounts of both calcium and potassium, and therefore straddles both classifications.
The most significant feldspars within the jewelry trade are labradorite, andesine, oligoclase, albite and orthoclase, with the latter two combining to form the well-known gem variety, moonstone. In addition, the presence of tiny, plate-like inclusions of copper, goethite or hematite within oligoclase or, more rarely, orthoclase gives rise to the spangled effect of sunstone.
Visual Observations: Tetrahedral 2-phase inclusions, color zoning. Often moderate to strong fluorescence. Variety Blue John: massive with banding.
Hardness: 4
Treatments: None
Fluorite is the mineral form of calcium fluoride, which is noted for its wide range of industrial applications and occasional use as an ornamental material. It produces crystals that are often large in size and flawless, as well as possessing a wide variety of highly saturated hues. However, due to fluorite’s very low hardness (4.0) and vulnerable directional cleavage, faceted specimens are intended more as a collector’s stone rather than for use within gem-set jewelry.
Attractive microcrystalline forms of fluorite are also encountered, with the most famous example being “Blue John” from Derbyshire, England and, more recently, China’s Zhejiang Province. This material contains contrasting bands of purple, yellow and white, and was especially popular during the nineteenth century when it was primarily used for fashioning into drinking vessels and other receptacles.
Garnet (All varieties)
Rather than merely being one single mineral species, the garnet family consists of six fundamental sub-species with identical crystal structures. As a result, despite their differing compositions, the garnets tend to possess similar visual and physical attributes.
The three aluminum-containing sub-species are often classified together under the portmanteau “pyralspites”, with the abundant pyrope and almandine garnets possessing the dark red hues traditionally associated with the gemstone. However, spessartine is instead noted for its orangish coloration, with pure orange material sometimes sold under the trade name “mandarin garnet”.
The three remaining sub-species are termed “ugrandites”, and these all contain calcium within their fundamental compositions. While uvarovite’s bright green crystals are too small for mainstream jewelry use, similarly colored grossularite (tsavorite) and andradite (demantoid) are amongst the best-known and most valuable of all green gemstones. In addition, yellowish, orangish, reddish and/or brownish grossularite (hessonite) is also commonly encountered within the marketplace.
While the term "goshenite" was previously also applicable to beryl with a very pale, yet perceptible, hue, it is now only used for material that appears completely colorless. As such crystals lack the impurities responsible for the colors seen in emerald, aquamarine and morganite, goshenite represents beryl in its purest form.
First described from material found close to Goshen, Massachusetts, goshenite’s relative abundance - especially when combined with the fact that beryl are usually prized for their body colors alone - means that only the largest and most transparent crystals are faceted for collectors, and fewer still are included within gem-set jewelry. However, this is also true for most other colorless crystalline minerals, as they are almost invariably deemed to be inferior to diamond in terms of their visual appearance, durability, rarity and perceived value.
Hibonite is a complex oxide, which has become highly sought after by collectors of rare minerals. It was first discovered in 1956 by the French prospector Paul Hibon in Madagascar, with additional deposits subsequently found in Russia and, as recently as 2011, within Myanmar’s famous Mogok gemstone tract. While hibonite crystals sourced from the former two localities tended to be a very dark brown that verged on black, the Burmese material possesses sufficient size, clarity and lightness of tone so as to be suitable for faceting. However, as is often the case with rare minerals, these specimens generally carry more value in their natural form and only around ten cut stones are known to exist.
Microscopic blue crystals of extra-terrestrial hibonite have also been found in meteorites, with the most famous example being the 1.5 mm “Blue Angel” from the Murchison meteorite that impacted Victoria, Australia in 1969.
Hiddenite is a variety of spodumene, which is defined by its yellowish and/or greenish color. This coloration results from the presence of chromium within the spodumene structure. However, because spodumene crystals are strongly pleochroic, the observed hue will depend on the stone's orientation or the angle from which it is viewed.
The gemstone has a relatively short history, having been discovered by W. E. Hidden towards the end of the nineteenth century in Alexander County, North Carolina. This deposit continues to be a key hiddenite source, but gem-quality material has also since been found in Afghanistan, Madagascar and Brazil.
It should be noted that some purple or lilac kunzites will turn green when irradiated. However, this material is not hiddenite, and the green coloration fades very quickly upon exposure to light.
Visual Observations: Commonly dyed blue but Untreated color is white, may be spiderweb matrix.
Hardness: 3.5
Treatments: Dyed, Impregnation
Howlite is a calcium-containing borosilicate, which is most commonly used to simulate a variety of more valuable ornamental materials. Occurring as cauliflower-like microcrystalline masses, the mineral is very suitable for this purpose as its whitish coloration and high level of porosity allows for the easy and effective absorption of dyes. In addition, because some specimens also possess dark veining, dyed howlite can be especially convincing when used as an inexpensive turquoise simulant. However, it should be noted that these two materials are completely unrelated to each other, so the term “white, turquoise” is a misnomer.
The mineral was first discovered in 1868 by the Canadian geologist Henry How in his native Nova Scotia, but California is the primary source of howlite today. These are also the only two localities in the world that produce the rare colorless macrocrystals, which can grow up to one centimeter in length.
Iolite
Visual Observations: Often eye-visible pleo with plate like finger print
Hardness: 7 - 7.5
Treatments: None
Derived from the Greek meaning “violet”, iolite is the gemological term for the mineral cordierite. While cordierite can be found in other hues, iolite gemstones are almost always blue. Previously known as dichroite, this material is noted for its very strong pleochroism, with a stone’s cutting orientation and/or the angle from which it is being viewed determining whether a deep violetish-blue, yellowish-gray or very pale blue coloration is observed. In fact, iolite's appearance in the latter near-colorless direction has led to it sometimes being known by the misnomer of “water sapphire”.
One interesting historical use for iolite was as a primitive polarizing lens to help sailors locate the position of the sun on an overcast day. This, in combination with the water-like appearance described above, has led to the gemstone becoming inextricably linked with seafaring cultures.
As with many of the vague terms used to describe the various microcrystalline quartz forms, the exact definition of “jasper” has never been officially determined.
However, with a name derived from the Old French for “spotted or speckled stone”, most jaspers include more than one color and the various sub-variety names often describe what the resulting color patterns most closely resemble (e.g., leopard skin jasper, orbicular jasper, ribbon jasper, zebra jasper, poppy jasper, etc.).
While the above could also be equally applicable to agates, it is the stone’s translucency, or a lack thereof, that differentiates these two chalcedony groups, with most varieties of jasper being completely opaque. This distinction can be most clearly seen when comparing the visual appearances of opaque moss jasper and the similarly named, translucent moss agate.
Jeremejevite
Visual Observations: Very light in tone and have hollow tube with light inclusion.
Hardness: 6.5 - 7.5
Treatments: None
The aluminum borate, jeremejevite, is one of the world’s rarest gemstones.
Named after Russian mineralogist Pavel Vladimirovich Jeremejev, the mineral was originally discovered in his homeland's Trans Baikal region in 1883. However, despite the relatively large size of these initial Russian jeremejevite crystals, their lack of color prevented the find from creating any significant waves within the gem trade at the time. This situation changed in 1973, with the discovery of facet-quality, cornflower blue material at Namibia’s coastal Mile 72 campsite, and then further inland within the Erongo Mountains.
While jeremejevite is sufficiently hard for use as a jewelry-set gemstone, the lack of reliable and consistent production means that blue jeremejevite crystals of significant size will likely only be purchased by serious mineral collectors for displaying in their natural form.
Kunzite is a variety of spodumene, which is defined by its purple, violet, pink or lilac color. This coloration results from the presence of manganese within the spodumene structure. However, because spodumene crystals are strongly pleochroic, the observed hue and/or intensity will depend on the stone's orientation or the angle from which it is viewed.
The gemstone has a relatively short history, having been first described by George F. Kunz at the turn of the twentieth century in San Diego, California. However, most of the world's kunzite supply now comes from Afghanistan and neighboring Pakistan, while Madagascar and Brazil are also significant sources for the gem.
It should be noted that the hues of some kunzite gemstones may fade upon prolonged exposure to sunlight, with previously irradiated stones being especially prone to losing color in this way.
Visual Observations: Often used as sapphire imitation. Commonly zoned, may appear fibrous, often blue and colorless pleochroism.
Hardness: 4 - 7.5
Treatments: None
Alongside andalusite and sillimanite, kyanite is one of the three aluminosilicates that may occasionally be encountered as faceted or cabochon-cut gemstones. The mineral also has many important industrial uses, including as an ingredient within ceramic items that are likely to be exposed to high temperatures.
Kyanite’s most distinctive property is its differential hardness, which causes it to be very soft (4.5-5.0) in one direction and acceptably hard (6.5-7.0) perpendicular to this. When combined with the mineral’s vulnerable directional cleavage and typically uneven color distribution, this direction of extreme softness has somewhat limited kyanite’s popularity as a gemstone.
Named after the Greek word for “deep blue”, kyanite is almost always associated with the sapphire-like blue hues of the most prized Nepalese material and, to a lesser extent, light greens. However, Tanzania has recently started producing gem-quality orange crystals, which are colored by the presence of trace manganese impurities.
Visual Observations: Labradorescence often blue to green
Hardness: 6 - 6.5
Treatments: None
A member of the calcium- and sodium-containing plagioclase series of feldspars, the relative quantities of these two elements within labradorite ranges from roughly equal to around two-to-one in favor of calcium. As a gemstone, labradorite is noted for the multicolored, but primarily blue, adularescent effect that moves across its otherwise gray surface when then stone, viewer and/or light source is moved. In fact, this phenomenon is so distinctive that it is often referred to as “labradorescence”.
Labradorite was initially discovered in 1770 on Paul’s Island, which is located off the Canadian province from which it takes its name. However, the material has also since been found in Norway, Australia, Madagascar, Russia, Ukraine, United States (New York) and Finland, with the latter being the sole producer of an especially colorful variety known as “spectrolite”.
Larimar is a rare variety of the mineral pectolite, which is colored greenish blue to blue due to the replacement of some the mineral’s fundamental calcium content with copper. Most larimar also contains whitish streaks, with higher-value stones usually possessing a strong contrast between these and the adjacent deep blue regions.
In the early twentieth century, the as yet unnamed material was first discovered in the Dominican Republic by Father Miguel Domingo Fuertes Loren. However, his attempts to exploit the source were denied by local authorities who were unaware of the material’s existence. The deposit subsequently lay dormant for almost sixty years before being rediscovered by a member of the US Peace Corps and his local friend, with the latter naming the new gem material after his daughter, Larissa, in combination the Spanish word for “ocean”.
To this day, the Dominican Republic remains the world’s only source of larimar.
Visual Observations: Dark green with black mottled color
Hardness: 6
Treatments: None
A predominantly green metamorphic rock with blackish veining and/or mottling, maw-sit-sit was first discovered and identified by the renowned Swiss gemologist Eduard J. Gübelin during a 1963 expedition to northern Myanmar’s well-known jadeite deposits. It was subsequently named after a Burmese village located close to what was at the time, and still remains, the world’s only known source for the material.
As maw-sit-sit usually contains varying degrees of chrome-bearing green jadeite, it is sometimes also known by a variety of jade-related alternative names such as “chrome-jade” and “maw-sit-sit jade”. However, the primary constituent (~60%) within the material is the less well-known kosmochlor - a mineral that many prominent figures within the gemological industry believe should be officially designated as a “jade” alongside jadeite and nephrite. In addition, maw-sit-sit also contains small quantities of albite feldspar, eckermannite, chromite and natrolite.
Visual Observations: Commonly black maybe sheen
Hardness: 5 - 5.5
Treatments: None
Obsidian is a naturally occurring glass, which was formed from molten magma that cooled too quickly to solidify into a crystalline form. Although usually associated with a black coloration, it can also be somewhat reddish, brownish, orangish and/or greenish. However, brightly colored specimens sold as "red", "green" and, especially, “blue" obsidian are likely to actually be man-made glasses from China, as such hues do not occur in nature.
Having been used as a weapon and gemstone since ancient times, obsidian’s name is described within Pliny’s Naturalis Historia as having been derived from that of a Roman explorer who had previously discovered a similar-looking material in modern-day Ethiopia. However, obsidian sub-varieties are usually defined by their visual attributes, with the white cristobalite inclusions seen within “snowflake obsidian” being the best-known of these. Other examples include the spectral iridescent effect displayed by "rainbow obsidian" and the reddish-brown regions contained within "mahogany obsidian".
Onyx is a black variety of massive quartz (i.e., chalcedony), which may or may not also possess parallel white banding. However, most of the “black onyx” sold within the marketplace today is white or light gray chalcedony that has been “carbonized” in a sugar solution to turn it black. In addition, many other so-called “onyx” stones are not even chalcedony at all, with banded limestone being the most commonly encountered simulant.
The ancient Greeks and Romans prized onyx, as the black and white regions provided two contrasting colors for the carving of cameos and intaglios. The material was also very suitable for the art deco design style that was popular during the twentieth century’s interwar period, but the above-mentioned abuse of the name has since somewhat diminished the material’s reputation and value.
Visual Observations: May or may not have play-of-color. Key to separation from synthetic opal is "no snakeskin", "no columnar structure". Key to separation from imitations (glass,plastic) : RI and SG. May phosphoresce.
Hardness: 5 - 6.5
Treatments: Sugar, Smoke treated
Opals are composed of hydrated silica and can contain up to twenty percent water by weight. The material is usually sub-classified as either “precious” or “common”, depending on whether or not its surface is able to display the iridescent play-of-color effect for which the species is best known. In the case of common opals, this phenomenon is not present and such stones are usually discarded if they do not possess unusual or attractive visual characteristics.
When they are retained and sold, common opals are given a wide range of varietal names depending on their inclusions, body color and/or degree of transparency. These include “liver opal” (brownish), “prase opal” (yellowish-green and somewhat translucent), “jasper opal” (reddish-brown and opaque), “moss/dendritic opal” (contains plant-like inclusions) and “wax opal” (yellowish, with a waxy luster).
Orthoclase
While orthoclase is a relatively abundant potassium-containing feldspar, transparent crystals that are sufficiently large for faceting are comparatively rare. The mineral's name is derived from the Greek words for “right” and “fracture”, due to its two directions of vulnerable cleavage being orientated perpendicular to each other.
Until a source of gem-quality green crystals was discovered in northern Vietnam around the turn of the millennium, faceted orthoclase had typically only been found with pale yellow or colorless hues. The final cut stones from this new deposit were initially mis-sold as “faceted amazonite”, which is a well-known variety of microcline feldspar that had only previously been encountered as microcrystalline masses. However, further investigation determined that the crystals were in fact orthoclase, with these two chemically identical feldspars separable by way of their differing internal crystal structures.
Visual Observations: for many years, less than 10 specimens were known to exist. Several thousand painites from Mogok today.
Hardness: 8
Treatments: None
Painite is a borate of calcium, zirconium and aluminum, which was previously noted for its extreme rarity. This reputation was built upon the fact that not a single crystal of the mineral was found during the twenty-five years that followed its initial 1954 discovery in northern Myanmar’s famous Mogok gemstone tract.
Named after the English mineralogist and gemstone collector Arthur Charles Davy Pain, the rate of Mogok’s alluvial painite production has increased significantly in recent decades, but it is still sufficiently rare to be of interest to mineral collectors. This, in combination with its somewhat undesirable dark brownish-red hue and typically poor clarity, means that only a small percentage of painite crystals are sacrificed for faceting and subsequent inclusion within gem-set jewelry.
Pargasite
A relatively common member of the amphibole mineral group, pargasite is a commonly encountered collector’s mineral that is only very rarely faceted. Although also occurring in black and brown, most of the commercially significant material is bright green and often found in association with marble. In addition, some such marble specimens from Luc Yen, Vietnam and Myanmar’s famous Mogok gemstone tract may also contain red spinel octahedra.
First discovered at the beginning of the nineteenth century, pargasite is named after its original source locality of Pargas, Finland. Aside from the two Asian ruby localities mentioned above, northern Pakistan also produces bright green, chromium-rich crystals, while most of the occasionally faceted brownish material is sourced in Tanzania, Ethiopia and Canada’s Baffin Island.
Blackish pargasite crystals may sometimes be encountered as a third constituent within the well-known ornamental rock “ruby-in-zoisite”.
Pearl (Saltwater)
Visual Observations: Luster: s-metalic- dull. Gritty to teeth (most imitation smooth)
Hardness: 2.5 - 4
Treatments: Bleaching, Dyed, Irradiation, Heat treatment, Coating
Saltwater pearls are created naturally in response to a threatening and/or irritating entity randomly entering the shell of a marine mollusk, usually an oyster, after which the intruder is coated with layers of organic matter to seal it off from the vulnerable, soft-bodied organism. This process occurs relatively rarely in nature, and randomly encountered natural pearls have therefore always been extremely scarce. Historically, the most desirable and valuable natural specimens were “oriental pearls” from the Middle East’s Arabian Gulf and Red Sea, as well as the Gulf of Mannar between India and Sri Lanka.
However, in 1916 a “culturing” process was patented off Japan’s south coast, whereby the above chain of events could be initiated via human intervention to produce whitish Akoya pearls. These techniques were then employed in warmer tropical waters to produce larger varieties such as blackish Tahitian pearls and white, silver or gold South Sea pearls.
Visual Observations: Often light in tone. Confused with spodumene and euclase: optic character key to separation.
Hardness: 7.5
Treatments: None
Phenakite is a beryllium-containing silicate, which is most commonly encountered a collector’s mineral. However, despite possessing fairly high levels of brilliance, above-average hardness (7.5-8.0) and a lack of vulnerable directional cleavages, phenakite’s popularity as a faceted gemstone has been held back by the paleness of its yellowish, grayish, brownish or, rarely, rose-pink hues. In fact, the vast majority of faceted gemstones that do appear within the marketplace are completely colorless.
Due to the mineral’s visual similarity to crystalline quartz, it is named after the Greek for “deceiver”. In addition, African phenakite crystals are sometimes fashioned in such a way so as to resemble the octahedral crystal forms of diamond, but these can be easily identified by their lower-than-expected measurable values and lack of diamond’s characteristic triangular etch marks on the crystal faces.
Prehnite
Visual Observations: Commonly light green "celery" green
Hardness: 6 - 6.5
Treatments: None
The hydrated calcium aluminum silicate, prehnite, was named after the Dutch mineralogist and military commander Colonel Hendrik Von Prehn in 1788, and it is widely believed that this was the first instance of a new mineral being named in someone’s honor.
The vast majority of material possesses a yellowish-green coloration that is somewhat pale, but brighter specimens with a similar hue may also be encountered. Pink and blue prehnites are extremely rare, while orange crystals have recently been discovered within South Africa’s manganese mining fields.
Most prehnite is too translucent to be faceted, and is instead usually fashioned into cabochons, beads and carvings. As a material with a slightly less than ideal overall durability, such cutting styles also offer a certain degree of protection against scratching and chipping.
Defined as corundum in any color other than red - due to the fact that red corundum is instead referred to as ruby - sapphire is one of the four gemstones previously thought of as “precious”. However, this term is seldom used today.
The name sapphire is derived from the Greek word for “blue”, and this remains, by far, the color with which it is most associated. In fact, it is customary within the gem trade to only use the non-prefixed term in isolation when referring to a blue stone.
While India’s Kashmir region is history's most revered blue sapphire source, today’s finest royal blue and lighter cornflower blue stones are found in Myanmar and Sri Lanka respectively, with Madagascar having become the primary producer in terms of quantity. However, most of the lower-quality inky blue material is sourced from Australia, Nigeria or China.
Visual Observations: Colorless and yellow stones often fluoresce orange to pink. Confused with quartz, beryl and labradorite.
Hardness: 6 - 6.5
Treatments: Heat treatment, Irradiation, Coating, Diffusion.
The scapolite are a group of common calcium-containing silicates, which occasionally possess sufficient levels of transparency to be used as both faceted gemstones and uncut specimens for mineral collectors. This gemmy material is usually associated with yellow or purple hues and is therefore often confused with the similarly colored macrocrystalline quartz varieties, citrine and amethyst. However, scapolite can usually be distinguished by way of its yellowish fluorescent glow under long-wave ultraviolet light sources. Some cabochon-cut specimens are also able to display chatoyant effects, with these “scapolite cat’s eyes” usually possessing either a brownish-red or white coloration.
With a name derived from the Greek for “stick” or “stem”, skapos, scapolite is often encountered in long, slender forms. Gemmy crystals were first discovered in Myanmar’s famous Mogok gemstone tract, but have also since been found in Brazil, Mozambique and Madagascar.
Visual Observations: Luster: greasy - waxy Used as jade imitation.
Hardness: 2 - 6
Treatments: None
Rather than merely being one distinct mineral species, serpentine represents a range of silicates with slightly differing compositions, including antigorite, chrysotile and lizardite. In gemological terms, members of the serpentine group are best known as jade simulants, due to their somewhat similar visual appearance to nephrite. However, genuine nephrite can usually be separated by way of its significantly higher specific gravity and hardness.
Bowenite is an especially hard variety of translucent, green to bluish-green antigorite, which makes for a far more durable and visually appealing ornamental material than regular serpentine. It is named after the nineteenth century American geologist George T. Bowen, who first discovered the material in Rhode Island, and has also since been found elsewhere in the northeastern United States, as well as New Zealand and China. Another variety of antigorite, williamsite, possesses an attractive apple-green hue and is often sufficiently translucent for faceting.
Visual Observations: Often grey to brown, may have silky luster.
Hardness: 6 - 7.5
Treatments: None
Alongside the more common andalusite and kyanite, sillimanite is one of three aluminosilicates that may occasionally be fashioned into gemstones. The mineral also has many important industrial uses relating to ceramics, glassmaking, and the smelting of iron and steel.
While transparent, light-toned grayish, yellowish, brownish, greenish and/or bluish crystals are sometimes faceted, the most commonly encountered gem sillimanites are the cabochon-cut cat’s eye specimens. These are usually formed from a fibrous sub-variety known as “fibrolite”, and often possess a translucent dark gray or opaque reddish-brown coloration. However, near-colorless chatoyant material is also encountered with significantly higher levels of transparency.
Named after the nineteenth century American chemist Benjamin Silliman, most gem-quality sillimanite is sourced in Sri Lanka, India, Kenya and Myanmar’s famous Mogok gemstone tract. In addition, it has also been designated as the official state mineral of Delaware.
Sinhalite
Visual Observations: Confused with peridot; common RI and optic sign (sinhalite strongly negative) key to separation.
Hardness: 6.5 - 7
Treatments: None
Following its discovery in Sri Lanka, sinhalite’s olivine-like optical and physical properties initially led mineralogists to believe it to be a brownish variety of peridot. However, it was eventually determined that the crystals in fact belonged to a new mineral species, which came to be named after the Sanskrit word for the island upon it was first found, Sinhala. A few years later, a second source of facet-quality material was discovered within Myanmar’s famous Mogok gemstone tract, while pinkish crystals have also recently been reported from Tanzania.
In nature, sinhalite is almost always encountered in the form of rounded, water-warn pebbles, rather than a recognizable surviving crystal habit. As a result, rough material is usually identified by way of its distinctive absorption spectrum, which possesses four bands in the cyan/blue region as opposed to peridot’s three.
Visual Observations: Often used as imitation lapis lazuli
Hardness: 5 -6
Treatments: None
Sodalite is a massive blue silicate mineral that is commonly fashioned into cabochons, inlays or carvings. It is a minor constituent within the more valuable lapis lazuli, and the names of the two materials are sometimes used interchangeably by less scrupulous dealers. However, “poor man’s lapis” can be identified by its darker royal blue hue, white veining and incipient cleavage cracks in six directions, as well as lacking the brassy pyrite inclusions commonly associated with real lapis lazuli.
Unlike lapis, sodalite was not known to the ancient world and was only identified in 1811 from deposits in Greenland. However, the material was not commercially exploited until eighty years later, when a significantly larger source was discovered in Canada.
Hackmanite is a pinkish variety of sodalite that quickly fades to white. However, material from some localities will subsequently regain its color in sunlight.
Visual Observations: Often low saturation. Crstal habit often twin.
Hardness: 8
Treatments: None
With a name derived from the Greek for “red”, ruby’s technical definition as the red variety of the mineral corundum was actually decided upon relatively recently. As a result, modern gemology has since re-classified some history’s most famous “rubies” as red spinels.
First discovered around 500 AD, northern Burma’s Mogok deposits continue to produce the world’s finest “pigeon blood” material. However, when Myanmar temporarily cut itself off from the rest of the world during the 1960s and 1970s, the eastern Thai city of Chanthaburi became the world’s only viable ruby source. As the deposit's overly dark stones required heat-based treatments to make them saleable, this represented the dawn of today's high-tech gemstone enhancement industry.
While superior ruby localities have since been discovered in eastern Africa, especially within Mozambique, another legacy of this period remains with Chanthaburi’s continued status as the world’s foremost gemstone enhancement, cutting and trading hub.
Sphene
Visual Observations: Natural inclusions, confused with zircon and demantoid.
Hardness: 5 - 5.5
Treatments: None
Sphene is a titanium-containing silicate, which has recently become somewhat abundant as a gemstone since the discovery of several new deposits in Asia and South America. The crystals are usually greenish, yellowish and/or brownish in color, but can be differentiated from similarly colored peridots or grossular garnets by the flashes of rainbow-like “fire” that exceed even those seen in diamond. While the surfaces of a faceted sphene can be polished to the highest-possible adamantine luster grade, the mineral’s inherent softness (5.0-5.5) means that such a bright shine is difficult to maintain over time.
Due to the shape of its crystals, the mineral’s gemological name, sphene, is derived Greek word for “wedge”. However, the alternative name of titanate has been used within scientific circles for over two hundred years and remains the preferred choice for mineralogists.
Spodumene
Spodumene is a lithium-containing silicate, which was once the primary source of the metal and remains so when very high purities are required. Initially only associated with pale yellow to colorless hues, spodumene rose to prominence as a gemstone around the turn of the twentieth century after the discoveries of chromium-containing emerald-green hiddenite and manganese-containing pinkish-to-purplish kunzite. While spodumene crystals are typically large in size, their directions of vulnerable cleavage and/or parting tend to complicate the faceting process, and it should also be noted that the hues of some kunzites have been color-enhanced via heat treatment and may subsequently fade after prolonged exposure to sunlight.
The species’ rather unattractive name is derived from the Greek for “ash-colored”, spodumenos, in reference to the coloration of many of its crystals, while the above-mentioned gem varieties are named in honor of the prominent mineralogists George F. Kunz and William E. Hidden.
Visual Observations: Often translucent to opaque purple. Usually occur as aggregate; know in the trade as "Royal Lavulite" or "Royal Azel".
Hardness: 5.5 - 6.5
Treatments: Heat treatment, Irradiation, Coating, Diffusion.
Sugilite is a rare mineral, which is generally only found in the massive form. It possesses a purple, violet and/or pink hue, which is caused by its fundamental manganese content. Most material sold as ”sugilite” is actually a mixture of sugilite and chalcedony quartz, with the latter contributing attractive dark or light mottling, veining or layering against the former’s purple coloration. Making up just 0.05% of the overall production, the highly valuable pure sugilite has a translucent, gel-like appearance and is purple all over.
Brownish-yellow deposits of the mineral were first identified in 1944 by petrologist Ken-Ichi Sugi in his native Japan. However, it wasn’t until the accidental 1979 discovery of purple South African material within the Kuruman manganese mining fields that sugilite came to be regarded as a commercially viable ornamental material.
Taaffeite
Visual Observations: Color often grayed out. Very rare gem, may be confused with spinel.
Hardness: 8 - 8.5
Treatments: None
Taaffeite is a rare oxide, which is notable for being the only known mineral to contain both beryllium and magnesium within its fundamental composition. Usually, but not always, associated with pinkish, purplish and/or violetish hues, it is one of the world’s rarest gem materials.
The gemstone was named in honor of the Austrian gemologist Richard Taaffe, who in 1945 had purchased a faceted “spinel” from a Dublin jeweler. However, unlike what would be expected for a genuine spinel, the specimen was optically anisotropic and was therefore determined to belong to an entirely new species. As a result, taaffeite was, and remains, the only mineral to have been initially described from faceted samples, rather than while still in its natural form.
First discovered in 1967, musgravite is almost indistinguishable from taaffeite. The two minerals differ very slightly in their composition, with raman spectroscopy usually required to separate them.
Visual Observations: Untreated stones often are colorless.
Hardness: 8
Treatments: Heat treatment, Irradiation, Coating, Diffusion.
Topaz is a fluorine-containing silicate, which is commonly encountered as both a faceted gemstone and uncut crystal specimen. Although traditionally associated with yellowish and/or brownish hues, modern-day irradiation and subsequent heating of previously colorless material today produces the light “sky” blue, bright “Swiss” blue and dark-toned, grayish “London” blue varieties in huge quantities. At the opposite end of the rarity and price spectrum, reddish, pinkish and/or orangish “Imperial” topaz is by far the most valuable variety - especially when cut in such a way so as to display an intense pleochroic coloration at the stone’s outer extremities.
It is important to note that the term “topaz” was historically used for a wide variety of yellow gem materials prior to the introduction of the modern gemological definition, with the name itself derived from that of a well-known ancient peridot source locality, namely the Red Sea Island of Topazios.
Visual Observations: Often strong pleo.(eye- visible)
Hardness: 7 - 7.5
Treatments: Heat Treatment, Irradiation
The tourmalines are a large group of complex silicates, which can produce crystals in almost every basic hue. As a result, they have become the dominant mid-market gem species and, since the discovery of the neon blue Paraiba variety, also now have a significant presence at the high-value end of the market.
While 32 different tourmaline sub-species are recognized by the International Mineralogical Association, the vast majority of gem tourmalines are elbaite. Named after the Italian island of Elba, its various hues have been allocated gemstone tradenames, including rubellite (red/pink), indicolite (greenish blue/blue), verdelite (green), Paraiba (neon blue) and achroite (colorless), as well as a bi-colored, pink and green “watermelon” variety.
Of the remaining 31 tourmaline sub-species, only the black schorl, multi-colored liddicoatite and brownish dravite are of any gemological interest, with chrome-containing specimens of the latter possessing green hues that are amongst the brightest in the gem world.
Visual Observations: Untreated stones often are colorless.
Hardness: 6 - 7.5
Treatments: Heat treatment
Not to be confused with the well-known synthetic diamond simulant cubic zirconia, zircon is a zirconium-containing silicate with a variety of industrial and ornamental applications. The mineral contains small amounts of the radioactive elements' thorium and uranium, which slowly break down its crystalline structure over time in a process known as metamictization. This allows zircon crystals to be tested for their age via radiometric dating, with specimens from Western Australia found to be the oldest known minerals on earth.
With a name derived from an ancient Persian for “golden-colored”, zircon has been used as a gemstone since biblical times. Under its previous name of “hyacinth”, it is traditionally associated with reddish, orangish, yellowish and/or brownish hues, while blue is perhaps most commonly encountered today.
Colorless zircon is the most convincing natural diamond simulant but has now been superseded by the synthetic materials moissanite and the above-mentioned cubic zirconia.
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