Gemstone
Gem is any mineral that is highly prized for its beauty, durability,
and rarity. It is enhanced in some manner by altering its shape,
usually by cutting and polishing. Most gems begin as crystals of
minerals or as aggregates of crystals. Non-organic origin material (eg pearl, red coral and amber) with several crystal origin is also classified as precious stones.
HISTORY OF GEMS
The use of gemstones in human history goes back to the Upper Paleolithic Period (25,000–12,000 BCE). People were initially drawn by the bright colors and beautiful patterns of gems. When the shaping of stones for adornment first began, opaque and soft specimens were used. As shaping techniques improved, harder stones began to be cut into gems. Beads of the quartz varieties hard carnelian and rock crystal were fashioned in Mesopotamia (now Iraq) in the 7th millennium BCE. Records of the time suggest that people thought that stones had a mystic value—a belief that persists to the present.GEM MINING
Gemstone deposits form in different geological environments. Perhaps the best known are the “pipes” of kimberlite, from which most diamonds are recovered by the hard-rock methods of drilling and blasting. Other gems also recovered from the rock in which they form are quartz varieties, opal, tourmaline, topaz, emerald, aquamarine, some sapphires and rubies, turquoise, lapis lazuli, and chrysoberyl. Hard and dense gemstones that are impervious to chemical weathering are carried by water to placer deposits such as river beds, beaches, and the ocean floor. Placer mining techniques mimic the creation of the placer by separating denser minerals in running water. The simplest methods are panning and sieving, or passing gravel through a trough of flowing water with baffles at the bottom. The lighter material washes away but denser gemstones remain.FACETING
Gemstones can be shaped in several ways. Opaque or translucent semiprecious stones, such as agate and jasper, are tumble-polished, carved, engraved, or cut with a rounded upper surface and a flat underside. Grinding and polishing of flat faces on the stone is called faceting. Facets are placed in specific geometric positions at specific angles according to the bending of light within a particular GEM CUTS There are three basic types of facet cut: step (with rectangular facets), brilliant (with triangular facets), and mixed (a combination of the two). The first faceting probably involved diamond cutting in Italy prior to the 15th century. First, only the natural faces of octahedral diamond crystals were polished. stone. Transparent stones, such as amethyst, diamond, and sapphire, are faceted to maximize their brilliance and “fire” or enhance color. Although much material is ground away while cutting, the final value is much enhanced.GEM CUTS
There are three basic types of facet cut: step (with rectangular facets), brilliant (with triangular facets), and mixed (a combination of the two). The first faceting probably involved diamond cutting in Italy prior to the 15th century. First, only the natural faces of octahedral diamond crystals were polished. stone. Transparent stones, such as amethyst, diamond, and sapphire, are faceted to maximize their brilliance and “fire” or enhance color. Although much material is ground away while cutting, the final value is much enhanced. The rose cut was developed in the 17th century. By about 1700, the brilliant cut (today’s favorite for diamonds and other colorless gems) was created. The emerald cut was soon developed to save valuable material, as its rectangular cut conforms to the shape of emerald crystals. Today there are hundreds of possible gem cuts.Diopside
Diopside is a member of pyroxene group mineral with formula is MgCaSi2O6. Specimens can be colorless but are more often bottle green, brownish green, or light green in color. It has two distinct prismatic cleavages at 87 and 93° typical of the pyroxene series. Diopside occurs in the form of equant to prismatic crystals that are usually nearly square in section.
Sodalite
Sodalite is a feldspathoidal tectosilicate mineral that is rich royal blue widely used as an ornamental gemstone. Chemical formula is Na8 (Al6Si6O24) Cl2. Specimens can be blue, gray, pink, colorless, or other pale shades. They sometimes fluoresce bright orange under ultraviolet light. Sodalite nearly always forms massive aggregates or disseminated grains.
Opal
Opals are a unique and mesmerizing gemstone known for their distinctive play of color, making them one of the most sought-after and mysterious gemstones...
Corundum
Corundum is a mineral that is primarily composed of aluminum oxide (Al2O3) and is one of the naturally occurring crystalline forms of aluminum oxide....
Diamond
The hardest known mineral, diamond is pure carbon. Its crystals typically occur as octahedrons and cubes with rounded edges and slightly convex faces. Crystals may be transparent, translucent, or opaque. They range from colorless to black, with brown and yellow being the most common colors. Other forms include bort or boart (irregular or granular black diamond) and carbonado (microcrystalline masses).
Andalusite
Andalusite is a rock forming minerals and is an aluminium nesosilicate minerals with the chemical formula Al2SiO5.At higher temperatures and pressures, andalusite may convert to sillimanite.andalusite is an aluminosilicate index mineral, providing clues to depth and pressures involved in producing the host rock.
Obsidian
Obsidian is an igneous rock that forms when molten rock material cools so rapidly that atoms are unable to arrange themselves into a crystalline structure. It is an amorphous material known as a "mineraloid." The result is a volcanic glass with a smooth uniform texture that breaks with a conchoidal fracture .
Fluorite (Fluorspar)
Fluorite, also called fluorspar, common halide mineral, calcium fluoride (CaF2), which is the principal fluorine mineral. It is usually quite pure, but as much as 20 percent yttrium or cerium may replace calcium. Fluorite occurs most commonly as a glassy, many-hued vein mineral and is often associated with lead and silver ores; it also occurs in cavities, in sedimentary rocks, in pegmatites, and in hot-spring areas
Pyrite (Fool’s Gold)
Known since antiquity, pyrite is commonly referred to as “fool’s gold.” Although much lighter than gold, its brassy color and relatively high density misled many novice prospectors. Its name is derived from the Greek word pyr, meaning “fire,” because it emits sparks when struck by iron.
Spinel
Spinel is the name of both an individual mineral and of a group of metal-oxide minerals that share the same crystal structure. Minerals in this group include gahnite, franklinite, and chromite. Spinel is found as glassy, hard octahedra, or as grains or masses.
Hematite
Hematite is a mineral and a common form of iron oxide. It is known for its distinctive reddish-brown to black metallic luster. The name...
Malachite
Possibly the earliest ore of copper, malachite is believed to have been mined in the Sinai and eastern deserts of ancient Egypt from as early as 3000 BCE. Single crystals are uncommon; when found, they are short to long prisms.