Chrysoberyl: Chrysoberyl appears as prismatic, tabular crystals often v-shaped twins forming pseudo-hexagonal crystals. Single crystals are rare. May be colorless, green, yellow, gray or brown. A variety, alexandrite, is red in tungsten light but dark green in daylight. This pronounced color change is highly-prized, and the exact tone of colors is important, the ideal being brilliant green turning to fie (read full)

Iolite: Iolite is the violet-colored variety of Cordierite (named after French geologist P. Cordier), a silicate of aluminum and magnesium, with an orthorhombic crystal system. Though the name cordierite is used by mineralogists, the name iolite has become established among gemologists. It appears as stubby, prismatic crystals, pesudo-hexagonal twins with a glassy appearance. It is frequently microgranul (read full)

Goshenite Beryl: Goshenite is a colorless sodium-rich gem variety of Beryl, a group which includes Emerald and Aquamarine. Other gem beryls include Heliodor and Morganite. It also appears are pale-green, apple-green, to bluish. All beryls are resistant to chemicals with the exception of fluoric acid. They are brittle and therefore easily damaged by knocks, have a vitreous luster, and occur with aquamarine. Their (read full)

Staurolite: Staurolite is a hydrous magnesium aluminum silicate that crystallizes in the monoclinic system. It appears as coarse, dark gold-brown prisms, or sometimes reddish-brown to black stubby crystals. On weathered rock, it stands out in contrast like sand-coated yellowish brown prisms. Surfaces are often rough or covered with an earthy coating because of natural alteration. It frequently occurs in ch (read full)

Benitoite: Benitoite is a rare gemstone / mineral that fluoresces when lit by black lights. It gets its name from San Benito County, California where it was first found. This gem is almost always blue (it was originally thought to be a sapphire) but also has variations in purple, pink, and clear. Gem prices seem to fluctuate but a few hundred dollars per half ct is common. Why so expensive? The quality gem (read full)

Hauyne: Hauyne is a blue feldspathoid rock-forming mineral, one of four members of the sodalite mineral group that is a component of lapis lazuli. The other three are lazurite, sodalite, and nosean. It is a complex mineral of sodium, calcium, aluminum silicate, and sulfate. Hauyne forms very bright and attractive though uncommon transparent blue dodecahedral or pseudo-octahedral crystals of the cubic sy (read full)

Phenakite: Phenakite is a rare beryllium silicate with a hexagonal crystal system. It an attractive hard mineral that resembles quartz. It appears as white or colorless rhombohedral crystals or stubby prisms terminated by multiple rhombohedral faces. Twinned crystals are also common. It may be colorless, yellow, pink, or brown. There are occasional chatoyant specimens, and four-rayed star stones with a brow (read full)

Lazulite: Lazulite is a compact, pleochroitic mineral which forms a series to scorzalite. It is dichroic, with a monoclinic crystal system. It appears as pointed, pseudo-dipyramidal, bright blue crystals in microgranular masses. It is hard, medium heavy, fragile with indistinct prismatic cleavage. It is translucent, with vitreous luster. It is infusible, discolors and breaks into small fragments when heat (read full)

Scheelite: Scheelite is a mineral in the group of Sulfates, Chromates, Molybdates, Tungstates. It has the same crystal structure and outside appearance as powellite. But scheelite is a calcium-tungstate, while powellite is a calcium-molybdate.

In rocks, scheelite may appear as crystals like two pyramids connected at its bases, or pseudo-octahedral, or having table-like faces, with detectable p (read full)

Cassiterite: Cassiterite may form as short or slender prismatic, or bipyramidal, elbow-shaped crystals. It has a crystal surface reflecting light as in a mirror. They may occur as massive, granular, botryoidal, and reniform. When found in granular, banded, fibrous masses, it looks like wood. When found in groups of large bright crystals, it is usually called "diamond tin." A red variety cut for collectors is k (read full)

Smithsonite: Smithsonite is a mineral in the group of Nitrates, Carbonates, Borates, with a hexagonal crystal system. It appears uncommonly in rhombohedral or scalenohedral crystals. But most of the time it appears with curved faces, like a thick creamy aqua-green mixture poured on rock and left to aggregate in clusters shaped like bunches of grapes, rounded, kidney-like, or to form like elegant icicles, and (read full)

Cerussite: Cerussite is a colorless carbonate of the aragonite mineralogical classification. It appears as colorless or white crystals with grayish tints, elongated and generally twinned to form a reticulated network with 60-degree angles, as stubby, tabular crystals in star- or heart-shaped twins. It can also be grey, greenish, or blue as a result of inclusions, such as lead, or copper. Impure cerussite is (read full)

Taaffeite: Taaffeite is a very rare beryllium magnesium aluminum mineral. No other mineral has both beryllium and magnesium in its composition. It is one of the few gems to be discovered as a faceted stone instead of a rough, as most gemstones are. Rarely cut as a gem, taaffeite looks like a mauve-colored spinel, and its absorption spectrum is similar to it. But gemologists know they've found taaffeite when (read full)

Sphalerite: Sphalerite is a zinc iron sulfide mineral formed in an isometric system. It is trimorphous with wurtzite and matraite. All three have the same chemical compound but crystallize in three different forms. The most common crystal forms of sphalerite are in dodecahedrons and tetrahedrons, elegant three-sided formations, often twinned, and otherwise usually massive, thus looking like brownish-black or (read full)

Citrine: Citrine is an attractive type of quartz, which is the commonest mineral on the earth's surface. But citrine itself is an uncommon macrocrystalline variety. Its yellow color brought about by its iron hydrate content, its reddish yellow from a trace of ferric iron. It forms hexagonal prisms, terminated by pyramidal shapes. Its faces are often striated, and the crystals twinned and distorted, having (read full)

Epidote: Epidote is widespread, forms a continuous series of minerals, ending with clinozoisite, which contains no iron. It occurs as crystals elongated and often striated parallel to length, and also as massive, fibrous, or granular habits. Epidote has a yellow-green color, ranges from yellowish-greenish to greenish-black. It has vitreous luster, and is transparent to nearly opaque. It has one perfe (read full)

Pyrite: Pyrite is an iron sulphide mineral with a cubic crystal system and is dimorphous with marcasite. It occurs as cubic crystals with striated faces, or in the form of pentagonal dodecahedra, usually well-crystallized, either isolated or in small, often well-formed groups, or as "iron cross" twins. It is a characteristic, brassy-yellow or pale-gold color, opaque and with a metal luster. It sometimes (read full)

Titanite: Titanite is a very rare calcium titanium silicate that is an important ore of titanium. It is also called Sphene. Its crystals are very rare, brilliant, and sparkles like diamond. It appears as crystals that are prisms with pyramid tips, or stubby, wedge-shaped, flattened crystals, or tabular and platy. There are also titanite crystal twins that have grown side by side or interpenetrated, or in g (read full)

Spinel: Spinel is an extensive group of minerals in which magnesium may be replaced with iron, zinc, and above all, manganese. The hardness and fine colors of gem quality spinel, known as Noble Spinel, set it apart as a gem material from other types of spinel. It normally occurs as distinct octahedral crystals, as clusters also of octahedral habit, or as characteristic twins. The crystals are often iso (read full)

Dravite: Dravite also called Brown Tourmaline is a sodium magnesium-rich mineral in the Tourmaline group of silicates, with a hexagonal system. Other members of this group include elbaite (sodium lithium aluminum rich); schorl and buergerite (sodium iron rich); uvite (calcium magnesium rich); and liddicoatite (calcium lithium aluminum rich). A continuous solid solution series exists between uvite and dravi (read full)

Gypsum: Gypsum is the most common sulphate mineral. It is usually the first evaporite mineral to be precipitated form water due to its poor solubility. Varieties include Selenite (or "spectacle stone), which is colorless and transparent; Satin Spar, the fibrous, translucent form with silky luster, which when cut cabochon shows pearly chatoyant effects; Alabaster, used for ornaments, which is firm, fine-gr (read full)

Rhodochrosite: Rhodocrosite is a manganese carbonate, a mineral of the calcite series with a hexagonal crystal system. It is isomorphous with calcite and siderite. It occurs as semitransparent, rhombohedral crystals with poor luster, frequently saddle-shaped, growing into druses, or as concretionary masses, sometimes with irregular, contorted veining. It has low hardness and perfect rhombohedral cleavage. Norm (read full)

Emerald: Emerald is the most prized variety of the mineral Beryl. It sometimes fetches higher prices than diamond. It appears as pale green to bright green. Though it is the green variety of beryl, not all gem-quality green beryls are called emeralds; yellow-green stones are called "heliodors;"soft blue-green or even pale green specimens are called "aquamarines." The typical color of emerald is a bea (read full)

Microcline: Microcline is a silicate of potassium and aluminum, and an alkali member of the feldspar group. It is the phase of this compound that is stable at low temperature. The feldspars are major constituents of the rocks on the earth's crust and comprise some of the most important rock-forming minerals. The four feldspars - orthoclase, sanidine, microcline and anorthoclase - comprise a group called the (read full)

Zircon: Zircon is a zirconium silicate with a tetragonal crystal system, and also contains thorium and uranium. It appears as stubby, prismatic, isolated or sometimes dipyramidal, like two pyramids connected at their bases; or in twins, colorless to yellow, red, brown, gray or green, in irregular granules. It is very hard, heavy, with indistinct cleavage, and shell-like fracture. It is sometimes perfect (read full)