The hardness of the stone - is the ability to resist external mechanical stress (cutting, scratching). The definition of rock hardness plays an important role. The most convenient way to determine the hardness of minerals is the definition of Mohs. Minerals are in it to increase their hardness. For comparison with the benchmark ten minerals in the scale are some of the metals and other materials: 1 - talc - corresponds to the hardness of the graphite and lead, 2 - Plaster - corresponds to the hardness of the nail, gold, tin, aluminum, 3 - calcite - corresponds to the hardness of copper, silver, 4 - fluorite - corresponds to the hardness of platinum, zinc, iron, phosphor bronze, 5 - apatite - corresponds to the hardness of glass, nickel, mild steel hardened, 6 - orthoclase, 7 - quartz - corresponds to the hardness of hardened tool steel - file holder, osmium, 8 - Topaz; 9 - corundum; 10 - Diamond. Stained stone plays a significant role in his assessment. Getting acquainted with the stone, it is necessary to clearly discern color, tint, hue and color intensity. Colored minerals can be divided into two types. In one of the color of the stone is constant and does not depend on impurities, and from the chemical composition of the mineral. Such a coloring is called idiohromaticheskoy. It is inherent in the mostly opaque colored stones - lapis lazuli, hematite, malachite, etc. Another type of color to the presence of a chemical compound of a dye - an element able to give coloring minerals - called allohromaticheskoy. These elements include chromium, titanium, vanadium, iron, cobalt, manganese, nickel, copper, etc. These elements Academy Fersman called "dye peace." Ability to identify gems and work with them need to know about such as a stone, such as: the fragility - of the mineral property to crumble under the mechanical action, chemical resistance - the ability to resist the action of acids and alkalis, and withstand high temperatures, the density - the amount of matter in a certain volume, one of the main features determining stone; depravity - the presence of cracks in the stones, foreign inclusions, air bubbles, etc. depravity is an important feature when evaluating gemstones and largely change their physical properties. Transparency - the ability of a mineral to transmit light. According to Transparency minerals are divided into transparent, translucent (translucent) and opaque. On the transparency of gem depends largely on the cut stone and its value. Refraction - is characterized by the ratio of the velocity of light in passing it from the air in the crystal and back. On the refractive index of light mineral depends on its brilliance. Distinguishing minerals on shine, believe that they can have a shiny glass, diamond, metal floor. The ability to refract light and make faceting can emphasize the optical properties of stone and the play of light in it. Faceted stone is a convex polyhedron whose faces may be of different shapes and sizes. To imagine a faceted stone, you must have some idea about the shape and type of cut. The shape of cut stones are divided into round, oval, marquise, a square (square), square, pear, drops, diamonds. In addition, the permitted and special forms. Some stones that have rectangular or other shape with sharp edges, corners may be posecheny. There are seven basic types of cuts, not counting the special: a diamond, graded, mixed, rose, cabochon, wedges, tabular. According to the established traditions of each form correspond to certain types of cuts. But in turn, each of the forms of rocks can take most types of cuts. Type of cut can be caused by physical and optical properties of the stones (strength, opacity). Faceting "cabochon", for example attached, usually opaque and translucent stones. Diamond-cut granite diamonds of any shape. Each type has a variety of cuts. The most diverse brilliant cut. Cut is considered full when the stone is faceted top and bottom. If plotted on a rock face just above the cut is called a rose. Fully faceted stone is divided, as it were into two parts: the upper - and lower crown - a pavilion. Classification by nature, color, purpose and origin of the stones - a division of stones on the gems, colored, stones and organic. Gems is considered to be transparent minerals, colored or colorless, reaching a faceting. Colored stones believed translucent or opaque stones are receptive to a smooth cut and used for jewelry and decorative art for craft projects. Flower beds, suitable for art and decorative craft, called stones. Living organisms form organic stones.
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