Gemstone cutting

Optical Properties. The high refractive index (2.42 at 589.3 nm) and dispersion (0.044) are the basis for the brilliance and fire of a properly cut gemstone. The optical transmission out to 10.6 p.m for Type Ila diamonds makes possible windows for CO2 lasers and for devices such as were in the... 

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... 

The hardness, index of refraction, and transparency of gemstones determine the way they are cut and polished. Since ancient times gemstones have been shaped in two main styles (1) as faceted gems, with many plane polished sides called facets, or (2) as nonfaceted, rounded, and polished gems, known as cabochons. 

Tiger s eye is a yellow and brown-banded gemstone, and Hawk s eye is similar but with blue bands. Both come from South Africa and result from silicification of cross-fiber veins of crocidolite. Cut en cabachon, and parallel to the fiber length. Tiger s eye and Hawk s eye exhibit variations in sheen and color that arise from the not-quite-parallel arrangement of the intimately associated asbestos and quartz. 

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