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Another method of isolating certain stones is by the action of heat-rays. Remembering our lessons in physics we recall that just as light-rays may be refracted, absorbed, or reflected, according to the media through which they are caused to pass, so do heat-rays possess similar properties. Therefore, if heat-rays are projected through precious [...] Hardness is perhaps one of the most important features in a stone, especially those of the “gem” series, for no matter how colour, lustre, general beauty and even rarity may entitle a stone to the designation “precious,” unless it possesses great hardness it cannot be used as a gem or jewel. Consequently, the hardness of [...] |
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