Gem stones

Schmuck, m. ornament jewelry finery, schmiicken, v.t. adorn, decorate, dress, Schmuck-stein, m. gem, gem stone, -waren, f.pl. jewelry, jewels,... 

Sapphires are naturally occurring gem stones, and are transparent to translucent. We know from ancient records that they have always been highly prized. Natural sapphires are found in many igneous rocks, especially syenites and pegmatites. Alternatively, synthetic sapphires may be made by doping aluminium oxide AI2O3 with a chro-mophore. 

Quartz is found in several forms in all three major kinds of rocks—igneous, metamorphic, and sedimentary. It is one of the hardest minerals known. Geologist often divides quartz into two main groupings—course crystalline and cryptocrystalline quartz. Course crystalline quartz includes six-sided quartz crystals and massive granular clumps. Some colored varieties of coarse crystalline quartz crystals, amethyst and citrine, are cut into gem stones. 

Feldspars are the most abundant minerals in the earth s crust, accounting for about 60% of all igneous rocks. They are derivatives of silica in which about one-half or one-quarter of the silicon atoms have been replaced by aluminum. Feldspar is used in the manufacture of certain types of glass and pottery. Some feldspar crystals, such as moonstone (white perthilte), Amazon stone (green microcline), and multicolored labradorite, are used as gem stones and in architectural decorations. Some are used as a coating and filler in the production of paper. 

Table 9.1. Luminescence, Raman and LIBS parameters of several gem stones...

An exception is negative elasticity, whereby the price for certain usually very expensive luxury products markedly decreases as they become more available. Examples include gem stones, scarce fine fragrance materials such as animal musks, and other luxury items. Elastic behaviour is promoted by alternative competing sources of supply of the product, the number of uses possible for the material and the utility and value of the product to the customer. 

Corundum is found as an accessory mineral in the crystalline rucks such as crystalline limestone and dolomites, gneisses, schists as well as in the igneous rock types granite and syenite. Corundum syenites are found in Canada, especially in the Province of Ontario. Rubies have long been mined in Upper Burma both rubies and sapphires arc found near Bangkok, Thailand. Numerous localities in India furnish gem stones of high quality. 

Pegmatites represent a residual phase of igneous depositions, characterized by extremely coarse crystalline material, that results Ironi the presence of associated volatiles, e.g.. water vapor, carbon dioxide, sulfur dioxide, and others, which decrease tile viscosity and facilitate crystallization. Quartz, feldspar, and mica are the more common minerals found in this environment. but Mich bodies are also hosts for many rare minerals and several types of gem stones, e.g.. beryl, tourmaline, and topaz. 

When a chemist wants some very pure carbon he might think of using diamonds of gem stone quality. This, however, would be a mistake. The per-... 

Table 1 Uses of Alumina Solid alumina Furnace components Catalyst substrates Electronics substrates Electrical insulators Cutting tools Bearings Spark Plugs Arc lamp tubes Laser hosts Gem stones Alumina powders Abrasives Catalyst pellets Alumina coatings Oxidation protection of aluminum and aluminum alloys Capacitors Transisitors Bioceramics Alumina fibers Thermal insulators Fire retardation Alumina as a component of...

Dense alumina can also be made by melting, but the high-melting temperature of 2,054°C makes this process expensive and difficult to control. High-value materials such as gem stones and laser hosts can be made by adding various colorants such as chromium, titanium, iron, cobalt, and vanadium to the melt. 

Without impurities alumina is colorless. However, addition of transition metal ions to alumina leads to spectacular colors, gem stones, and practical applications such as ruby lasers. Many aspects of color are discussed in detail in [51]. 

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