A Mineral That Can Be Cut, Polished, and Sold for Profit Is a Gemstone.
gemstone, any of various minerals highly prized for dazzler, durability, and rarity. A few noncrystalline materials of organic origin (e.k., pearl, cherry-red coral, and amber) likewise are classified as gemstones.
Gemstones have attracted humankind since ancient times, and accept long been used for jewelry. The prime requisite for a gem is that it must exist beautiful. The beauty may lie in colour or lack of colour; in the latter case, farthermost limpidity and "fire" may provide the allure. Iridescence, opalescence, asterism (the exhibition of a star-shaped effigy in reflected light), chatoyance (the exhibition of a changeable lustre and a narrow, undulating band of white light), pattern, and lustre are other features that may make a gemstone beautiful. A jewel must also be durable, if the rock is to retain the smooth applied to it and withstand the wearable and tear of constant handling.
Britannica Quiz
(Bed) Rocks and (Flint) Stones
Diamonds may be a girl'southward best friend, merely what is that mineral's closest relative? Exam your cognition of rocks, minerals, and all things "yabba dabba doo" in this quiz.
In add-on to their employ as jewelry, gems were regarded past many civilizations as miraculous and endowed with mysterious powers. Dissimilar stones were endowed with different and sometimes overlapping attributes; the diamond, for example, was idea to give its wearer forcefulness in boxing and to protect him against ghosts and magic. Vestiges of such behavior persist in the modernistic do of wearing a birthstone.
Of the more than 2,000 identified natural minerals, fewer than 100 are used as gemstones and only sixteen have accomplished importance. These are beryl, chrysoberyl, corundum, diamond, feldspar, garnet, jade, lazurite, olivine, opal, quartz, spinel, topaz, tourmaline, turquoise, and zircon. Some of these minerals provide more than one type of gem; beryl, for case, provides emeralds and aquamarines, while corundum provides rubies and sapphires. In virtually all cases, the minerals have to be cutting and polished for use in jewelry.
Except for diamond, which presents special problems because of its very great hardness (see diamond cutting), gemstones are cut and polished in whatever of three ways. Agate, opal, jasper, onyx, chalcedony (all with a Mohs hardness of seven or less) may be tumbled; that is, they may be placed in a cylinder with abrasive grit and h2o and the cylinder rotated about its long axis. The stones become polished simply are irregular in shape. Second, the same kinds of gemstones may instead be cut en cabochon (i.eastward., with a rounded upper surface and a flat underside) and polished on water- or motor-driven sandstone wheels. Tertiary, gemstones with Mohs hardness of more than vii may exist cut with a carborundum saw and so mounted in a holder (dop) and pressed against a lathe that can be made to revolve with farthermost rapidity. The lathe carries a betoken or modest deejay of soft atomic number 26, which tin vary in bore from that of a pinhead to a quarter of an inch. The face of the deejay is charged with carborundum grit, diamond dust, or other abrasives, along with oil. Some other tool used to grind facets is the dental engine, which has greater flexibility and sensitiveness than the lathe. The facets are ground onto the stone using these tools and and so are polished as described above.
Of decisive significance for the modern treatment of gemstones was the kind of cutting known as faceting, which produces brilliance by the refraction and reflection of light. Until the late Middle Ages, gems of all kinds were simply cut either en cabochon or, particularly for purposes of incrustation, into flat platelets.
The first attempts at cutting and faceting were aimed at improving the advent of stones past covering natural flaws. Proper cut depends on a detailed knowledge of the crystal structure of a stone, even so. Moreover, it was only in the 15th century that the abrasive property of diamond was discovered and used (nothing else will cutting diamond). Afterwards this discovery, the art of cutting and polishing diamonds and other gems was developed, probably in France and the Netherlands beginning. The rose cut was developed in the 17th century, and the brilliant cut, now the general favourite for diamonds, is said to have been used for the first fourth dimension virtually 1700.
In mod gem cutting, the cabochon method continues to be used for opaque, translucent, and some transparent stones, such as opal, carbuncle, and and then on; only for nigh transparent gems (especially diamonds, sapphires, rubies, and emeralds), faceted cut is almost e'er employed. In this method, numerous facets, geometrically disposed to bring out the dazzler of low-cal and colour to the best advantage, are cut. This is washed at the sacrifice of material, often to the extent of half the stone or more, but the value of the gem is greatly increased. The four near common faceted forms are the vivid cut, the step cutting, the drop cut, and the rose cut.
In addition to unfaceted stones being cabochon cut, some are engraved. High-speed, diamond-tipped cutting tools are used. The rock is hand-held against the tool, with the shape, symmetry, size, and depth of cut being determined past centre. Gemstones tin also be made past cementing several smaller stones together to create i large jewel. See assembled precious stone.
In some cases, the colour of gemstones is also enhanced. This is accomplished by any of three methods: heating under controlled conditions, exposure to X rays or radium, or the application of pigment or coloured foil to the pavilion (base) facets.
In recent times various kinds of synthetic gems, including rubies, sapphires, and emeralds, have been produced. Two methods of fabrication are currently employed, one involving crystal growth from solution and the other crystal growth from melts.
The Editors of Encyclopaedia Britannica This article was nearly recently revised and updated by Adam Augustyn.
Source: https://www.britannica.com/science/gemstone
0 Response to "A Mineral That Can Be Cut, Polished, and Sold for Profit Is a Gemstone."
Post a Comment