Sapphire gemstone

It is produced artificially for use as a gemstone, but it is relatively soft. Star sapphires and rubies exhibit their asterism as a result of the presence of Ti02. 

Synthetic gemstone materials often have multiple uses. Synthetic mby and colodess sapphire are used for watch bearings, unscratchable watch crystals, and bar-code reader windows. Synthetic quartz oscillators are used for precision time-keeping, citizen s band radio (CB) crystals, and filters. Synthetic mby, emerald, and garnets are used for masers and lasers (qv). 

Several gemstone species occur in various colors, depending on the presence of impurities or irradiation-induced color centers. Examples are the beryl, comndum, and quart2 families. Quart2 has poor optical properties (RI = 1.55, DISP = 0.013), but becomes of gemological interest when it exhibits attractive colors. Any material can have its color modified by the addition of various impurities synthetic mby, sapphires, and spinel are produced commercially in over 100 colors (2). Synthetic cubic 2irconia has been made in essentially all colors of the spectmm (11), but only the colorless diamond imitation is produced commercially in any quantity. 

The two extremes of ordering in solids are perfect crystals with complete regularity and amorphous solids that have little symmetry. Most solid materials are crystalline but contain defects. Crystalline defects can profoundly alter the properties of a solid material, often in ways that have usefial applications. Doped semiconductors, described in Section 10-, are solids into which impurity defects are introduced deliberately in order to modify electrical conductivity. Gemstones are crystals containing impurities that give them their color. Sapphires and rubies are imperfect crystals of colorless AI2 O3, red. 

Cutting, grinding, and shaping stone, and in particular burnishing and polishing the surface of stone as well as metals, requires the use of abrasive materials that are harder than the solids to be cut, ground, burnished, or polished. Sapphire and ruby, two very hard gemstones, for example, can be cut or polished only with the assistance of diamond powder, an abrasive that is harder than sapphire or ruby. Diamond is the hardest material... 

Ruby and Sapphire. Ruby and sapphire are "sister stones" both are gemstone forms of the mineral corundum (composed of aluminum oxide). Pure corundum is colorless, but a variety of trace elements cause corundum to exhibit different colors. Ruby is red corundum, while sapphire is corundum in all colors except red. The red in rubies is caused by trace amounts of chromium the more intense the red color of a ruby, the more chromium it contains. The blue in sapphires is caused by titanium and/or iron impurities (Garland 2002 Hughes 1997). 

An aluminum ion carries a 3+ charge, and an oxide ion carries a 2— charge. Together, these ions make the ionic compound aluminum oxide, AI203, the main component of such gemstones as rubies and sapphires. Figure 6.10 illus-... 

Several gemstone species occur in various colors, depending on the presence of impurities or irradiation-induced color centers. Any material can have its color modified by the addition of various impurities synthelic ruby, sapphires, and spinel are produced commercially in over 100 colors. 

Aluminum occurs in many common minerals and clays, as well as in gemstones. Sapphire and ruby are both impure forms of AI2O3 and receive their color from the presence of small amounts of other elements (Cr in ruby Fe and Ti in sapphire). Most aluminum is currently obtained from bauxite, A1203 H20, which occurs in large deposits in Australia, the United States,... 

A number of oxides are economically important ore minerals, such as hematite (iron), chromite (chrome), zincite (zinc), and cassiterite (tin). Some gemstone species are oxides, including corundum (ruby and sapphire), spinel, and chrysoberyl. Corundum is the second hardest natural substance and is used as an abrasive. 

---