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Gemstone Glossary

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Agate: A banded and often translucent form a chalcedony (microcrystalline quartz)

  • Mohs Hardness: 6.5 - 7
  • Specific Gravity: 2.63

Amazonite: A intrusive igneous variety of microcline potassium feldspar that typically forms in association with granitic rocks. Amazonite commonly found in China, Libya, Mongolia, South Africa and in the USA in Colorado, Virginia, and Pennsylvania.

  • Mohs Hardness: 6-6.5
  • Specific Gravity: 2.56 - 2.58

Amethyst: Amethyst is a silicate mineral and is a member of the quartz family. Amethyst contains small amounts of manganese that are responsible for the purple color when exposed to ultraviolet light.

  • Mohs Hardness: 7
  • Specific Gravity: 2.65

Apatite: A phosphate mineral found in igneous, metamorphic, and sedimentary rocks. The most prolific deposits of apatite are found in ancient marine and lakebed environments and consist of mineralized debris from water-dwelling organisms. Apatite gemstones can vary from translucent to opaque and with vivid green, yellow, and blue colors, depending on their chemical composition. It is commonly used as an index mineral because pure apatite is near a perfect five on the Mohs Hardness Scale.

  • Mohs Hardness: 5
  • Specific Gravity: 3.16 - 3.22

Beryl: A mineral classification that encompasses a number of semi-precious gemstones including emerald, morganite, aquamarine, heliodor and some other minerals.

  • Mohs Hardness: 7.5 - 8
  • Specific Gravity: 2.75

Bronzite: A magnesium-iron rich member of the pyroxene mineral group and is similar to enstatite and hypersthene. Bronzite is abundant in mafic igneous and metamorphic rocks and is commonly metallic brown, but can also be green when associated with the mineral olivine.

  • Mohs Hardness: 5.5
  • Specific Gravity: 3.3 - 3.4

Calcite: A form of calcium carbonate (CaCO3) that is the primary constituent of limestone. Calcite is considered an 'all-pervading' mineral as it is found almost everywhere in the world. Calcite can for form from the precipitation of calcium carbonate in seawater, in hydrothermal veins, or from the diagenesis of shells and skeletal parts of marine organisms. 

  • Mohs Hardness: 3
  • Specific Gravity: 2.7

Chalcedony: A microcrystalline type of quartz. Agate, jasper, and onyx are all forms of chalcedony.

  • Mohs Hardness: 6.5 - 7
  • Specific Gravity:¬†2.64

Chrysoprase: A cryptocrystalline form of chalcedony, meaning that it contains crystals so small that they cannot be discerned under normal magnification. It shows a minty to dark green color and can vary from being translucent to opaque.

  • Mohs Hardness: 7
  • Specific Gravity: 3.98

Clevage: A geological term that describes a minerals structural tendency to break along plains at certain angles. Types of clevage include basal, cubic, prismatic, conchoidal, uneven, etc. Cleavage is described by 5 qualitative terms relating to how 'clean' a clevage break shows: perfect, good, poor, indistinct, and none. While Mohs hardness is the best indicator of scratch resistance, a minerals clevage plays a larger roll in a stones overall durability and resistance to cracks and breaks.

Cubic Zirconia (CZ): A synthetic material that looks similar to diamond, although it can come in a variety of colors. CZ is extremely heavy, with a specific gravity upwards of 6 g/cm3, which is more that twice that of quartz. Production of CZ started in 1976 as a competitor to diamonds.

  • Mohs Hardness: 8 - 8.6
  • Specific Gravity: 5.6 - 6.0

Dendritic Agate: A silicate mineral containing manganese and iron branching that often resembles plant life. It can be both transparent or opaque and is typically colorless or cloudy white with black to brownish internal structures. 

  • Mohs Hardness: 6.5 - 7
  • Specific Gravity: 2.63

Dumortierite: An opaque alumino boro-silicate mineral that forms naturally in fibers and columnar crystals in high-temperature metamorphic rocks. Colors of dumortierite can vary from blue, brown, green, and pink in rarer cases. Dumortierite is relatively abundant and is found in many European countries and Russia, Namibia, Madagascar, and Sri Lanka. 

  • Mohs Hardness: 7
  • Specific Gravity: 3.3 - 3.4

Fluorite: Referred to as fluorspar and is a mineral variation of calcium fluoride (CaF2). Fluorite is a member part of the halide mineral group, forming in areas that contain felsic igneous rocks. Fluorite commonly develops in vein deposits by hydrothermal activity (sources of hot water that reside in the earth’s crust). Fluorite’s neighboring crystals during this common formation can include quartz and calcite.

  • Mohs Hardness: 4
  • Specific Gravity: 3.2 - 3.5

Garnet: A metamorphic silicate mineral that can range in color including yellow, green, orange, and red. Garnet is a metamorphic index mineral used by geologist to indicate high-grade metamorphism. Garnet in it's natural crystal form it typically quite smooth, however, when crushed it is very abrasive and is used commercially for sand blasting and as grit for very fine high sandpaper.

  • Mohs Hardness: 6.5 - 7.5
  • Specific Gravity: 3.62 - 3.87

Howlite: A borosilicate mineral found in evaporite deposits often in association with gypsum. Howlite is white with black vein structures. Because of its porous structure it takes well to dyes and it is commonly used to mimic other stones.

  • Mohs Hardness: 3.5
  • Specific Gravity: 2.53 - 2.59

Hypersthene: An inosilicate mineral containing both magnesium and approximately 50% iron. Hypersthene forms in both igneous and metamorphic rocks and is found in upstate New York as well as in parts of the Northeastern Canadian provinces.

  • Mohs Hardness: 5 - 6
  • Specific Gravity: 3.45 - 3.55

Iolite: A translucent form of the cyclosilicate mineral Cordierite, displaying a light blue color with a purplish hue. Iolite commonly occurs in in metamorphic rocks, but is also found in association granites and pegmatites. Nearby accessory minerals often include hornfuls and micas.

  • Mohs Hardness: 7 - 7.5
  • Specific Gravity: 2.6 - 2.7

Jasper: An opaque form of chalcedony(cryptocrystalline quartz). There are many different types of jaspers and they are commonly known for having multiple intertwined color patterns, however, the can be a solid color as well. 

  • Mohs Hardness: 6.5 - 7
  • Specific Gravity: 2.5 -2.9

Kunzite: A variety of the mineral spodumene. Kunzite is a delicate pale pink color and was first discovered by George Frederick Kunz who named it after himself in 1902. George was a distinguished mineralogist and at that time was the head jeweler at Tiffany & Co. Kunzite can be found in North and South America, as well in parts of Europe, Australia, and the Middle East.

  • Mohs Hardness: 6.5 - 7
  • Specific Gravity: 3.18

Kyanite: A blue aluminosilicate mineral that is most commonly found in metamorphic rocks, often in association with schist. Kyanite forms naturally in columns, fibers, or blades, and is used by geologist as an index mineral indicating high pressure and low temperature metamorphism.

  • Mohs Hardness: 4.5 - 7
  • Specific Gravity: 3.5 - 3.7

Lepidolite: A  grey to purple and sometimes red member of the phyllosilicate mica mineral group. Lepidolite is an abundant lithium bearing mineral that is sometimes used as a source for lithium metals.

  • Mohs Hardness: 2.5 - 3
  • Specific Gravity: 2.8 - 2.9

Malachite: A banded green opaque copper carbonate mineral that forms naturally in botryoidal clusters that look like a small bunch of grapes. Botryoidal Malachite is similar to a pearl in the sense that it forms radially around a nuclei such as a piece of sand or dust. As layers of malachite material form around the nuclei it forms a sphere, and when these spheres grow together it results in the botryoidal cluster that we see in raw form malachite specimens. 

  • Mohs Hardness: 3.5 -4
  • Specific Gravity: 3.6 - 4

Mohs Hardness Scale: A qualitative scale characterizing the scratch resistance of minerals. The scale ranges from 1 - 10, with 1 being the softest and 10 being the hardest. Don't confuse hardness with resistance to breaking, as a minerals 'cleavage' plays a larger role in overall durability.

Moonstone: An often translucent and sometimes cloudy stone composed of orthoclase feldspar and albeit. Moonstone displays a scattering of light between its mineral fabric layers knows as adularescence - a phenomenon that gives it a cats eye effect, and iridescent glow at changing angles.

  • Mohs Hardness: 6 - 6.5
  • Specific Gravity: 2.6

Nephrite: A dense dark green form of the mineral jade, often containing black inclusions. Nephrite jade, as well as it's counterpart jadeite, lack cleavage plains making then very durable and resistant to breaking. 

  • Mohs Hardness: 6 - 6.5
  • Specific Gravity: 2.95¬†

Obsidian: A naturally occurring volcanic glass resulting from rapid cooling of lava with minimal crystal growth. 

  • Mohs Hardness: 5 - 6
  • Specific Gravity: 2.4

Peridot: A gemstone quality variation of the magnesium-iron rich silicate mineral olivine. While olivine is common on every continent, gem-quality peridot is rare as it is not chemically stable on the Earth's surface. Peridot is found in mafic igneous rock deposits, however, it can also be found in meteorites.

  • Mohs Hardness: 6.5 - 7
  • Specific Gravity: 3.3

Pietersite: A brown to dark blue brecciated form of Tiger's Eye with a finer crystal structure and dark amphibole fibers. It is commonly referred to as a swirling mixture of Tiger's Eye and Hawk's Eye as they are pseudomorphs of one another. Pietersite can be found in Namibia and China.

  • Mohs Hardness: 6.5 - 7
  • Specific Gravity: 2.66

Quartz: Pure quartz is SiO2 (Silicon Dioxide) and it is the most abundant mineral on the earth's surface. While quartz is a transparent material that exudes prism crystal habit, it is also the base material for many other silicate minerals. 

  • Mohs Hardness: 7
  • Specific Gravity: 2.65

Rutilated Quartz: A form of quartz containing needle like inclusions of the mineral rutile. White the name rutilated quartz refers specifically to quartz containing rutile, the term is often used synonymously with tourmalated quartz because of the similarities in the appearance of the needles. 

  • Mohs Hardness:¬†7
  • Specific Gravity: 2.65

Specific Gravity: A measure of density in g/cm3. These numbers can be used for reference as to a gemstones weight. The larger the value indicates a higher density and heavier stone.

Tiger's Eye: Tiger's Eye is a metamorphic chatoyant ferro-silicate gemstone with golden to reddish-brown banding.

  • Mohs Hardness: 6.5 - 7
  • Specific Gravity: 2.58 - 2.64

Unakite: A metamorphic rock formed by hydrothermal alteration of granite. It is composed predominantly of pink orthoclase feldspar, green epidote, and quartz.

  • Mohs Hardness: 6 - 7
  • Specific Gravity:¬†2.85 - 3.2

Variscite: A green aluminum phosphate mineral that forms in aluminum rich rocks from the precipitation of phosphates in ground water. Variscite is sometime confused with turquoise due to it's similar color and structure. 

  • Mohs Hardness: 4.5
  • Specific Gravity: 2.57 - 2.61

Watermelon Tourmaline: A form of tourmaline that has form in spherically with red at it's center and green on the outside resembling watermelon and it's rind. Watermelon tourmaline is often translucent and it considered to be one of the more colorful tourmaline varieties.

  • Mohs Hardness: 7 - 7.5
  • Specific Gravity: 3 - 3.2

Zircon: A nesosilicate (ZrSiO4) accessory mineral found in igneous and metamorphic rocks. Zircon is mostly colorless, but it can also come in shades of yellow, orange, and red. 

  • Mohs Hardness: 7.5
  • Specific Gravity: 4.6 - 4.7 (very heavy)