Gemological Terminology
Banded Agate
 
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Agate Agate is a term applied not to a distinct mineral, but to an aggregate of various forms of silica,  mainly chalcedony.
Amorphous Solids An amorphous solid is a solid in which there is no long range order of the positions of the atoms. (Solids in which there is long-range atomic order are called crystalline solids or morphous).
Aquamarine Aquamarine is a gemstone-quality transparent variety of Beryl, having a delicate blue or Turquoise color, suggestive of the tint of seawater. It is closely related to the gem Emerald. Colors vary and yellow Beryl (Heliodor), rose pink Beryl (Morganite), and white Beryl (Goshenite) are known.
Asterism Asterism like Chatoyancy is the product of silky fine inclusions, when parallel to each other and oriented in multiple directions within a crystal, a cabochon cut stone will show beams of light for each of the sets of parallel inclusions. Examples Star Ruby and Star Sapphire.
Beryl The mineral Beryl is a beryllium aluminum cyclosilicate. It has a vitreous luster and can be transparent or translucent. Pure beryl is colorless, but it is frequently tinted by impurities; possible colors are green, blue, yellow, red, and white. The name comes from the Greek Beryllos which referred to a precious blue-green color of sea water stone. It is found under names like Emerald. Colors vary and yellow-green Beryl (Heliodor), rose pink beryl (Morganite), clear bright yellow Beryl (Golden Beryl) and white Beryl (Goshenite) are known.
Bixbite Bixbite is a form of the mineral Beryl is a beryllium aluminum cyclosilicate. Red Beryl is rare and has only been reported from a handful of locations.  The greatest concentration of gem-grade Red Beryl comes from the Violet Claim in the Wah Wah Mountains of mid-western Utah, discovered in 1958 by Lamar Hodges, of Fillmore, Utah, while he was prospecting for Uranium. Red Beryl is Bixbite or "Red Emerald" or "Scarlet Emerald," Bixbite should not be confused with Bixbyite.
Cabochon Cabochon is a gemstone which has been shaped and polished as opposed to facetted. The resulting form is usually a convex top with a flat bottom. The cutting of a cabochon is usually done to opaque gemstones, while faceting is usually done to transparent gemstones.
Chalcedony Chalcedony is a cryptocrystalline form of Silica, composed of very fine intergrowths of the minerals Quartz and Morganite. These are both Silica minerals, but they differ in that Quartz has a trigonal crystal structure, while Morganite is monoclinic. Often seen under common names such as Agate, Chrysoprase, Carnelian, Heliotrope, Blood Stone, Onyx and others.
Chatoyancy Chatoyancy is when minerals have a silky sheen that results from closely packed parallel fibers or parallel needle like inclusions. The result on a cabochon cut stone with a single light source is a band of light that moves across the surface of the stone as you change the relation to the light source. Example, Cats Eye, Tigers Eye.
Crystallography Crystallography  is the experimental science of determining the arrangement of atoms in solids. It is the scientific study of crystals.
Cryptocrystalline Cryptocrystalline is a rock texture which is very finely crystalline. In other words,  made up of such minute crystals, that its crystalline nature is only vaguely revealed even under microscopic examination.
Crystal While the term "Crystal" has a precise meaning within Material Science, while more commonly "crystal" refers to solid objects that exhibit well-defined and often pleasing geometric shapes. In this sense of the word, many types of crystals are found in nature.
Diatoms Diatoms are a major group of algae, and are one of the most common types of phytoplankton. Most diatoms are unicellular, A characteristic feature of diatom cells is that they are encased within a unique cell wall made of Silica (hydrated silicon dioxide). Fossil evidence suggests that they originated during, or before, the early Jurassic Period.
Emerald Emeralds are a variety of the Mineral Beryl colored Green by trace amounts of  Chromium and sometimes Vandium. Beryl has a hardness of 7.5 - 8 on the 10 point Mohs scale of mineral hardness. Most emeralds are highly included,  so their brittleness (resistance to breakage) is classified as generally poor.