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An asterism (from Ancient Greek ἀστήρ (astḗr) 'star' and -ism) is a star-shaped concentration of light reflected or refracted from a gemstone. It can appear when a suitable stone is cut en cabochon (i.e. shaped and polished, not faceted). A gemstone that exhibits this effect is called a star stone or asteria.
This is a list of gemstones, organized by species and types. Minerals. There are over 300 types of minerals that have been used as gemstones. Such as: A–B
Lapidary (from the Latin lapidarius) is the practice of shaping stone, minerals, or gemstones into decorative items such as cabochons, engraved gems (including cameos), and faceted designs. A person who practices lapidary techniques of cutting, grinding, and polishing is known as a lapidary or lapidarist .
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A gemstone (also called a fine gem, jewel, precious stone, semiprecious stone, or simply gem) is a piece of mineral crystal which, when cut or polished, is used to make jewelry or other adornments.
The natural formation of gemstones tends to layer the minerals in regular crystalline sheets, whereas many synthetically produced gems have an amorphous structure, like glass. Synthetics made by the Verneuil process either do not show flaws at all, or if any flaws are present, show curvy, undulating surfaces rather than flat ones.
As a general rule, a cut gemstone will reduce the mass (in carats) by about 50%. [1] Among the several techniques used to work with gemstones are sawing, grinding, sanding, lapping, polishing, grilling, and tumbling. The diamond cut planning stage is a complex process that requires the cutter to work with unique rough stones.
Main sapphire-producing countries. Sapphire is a precious gemstone, a variety of the mineral corundum, consisting of aluminium oxide (α-Al 2 O 3) with trace amounts of elements such as iron, titanium, cobalt, lead, chromium, vanadium, magnesium, boron, and silicon.