September 5, 2005

Quartz A colorless, transparent rock-forming mineral with vitreous luster, crystallizing in the trigonal trapezohedral class of the rhombohedral subsystem; hardness is 7 [...]
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September 5, 2005

Lapis-lazuli Lapis lazuli is one of the oldest of all gems, with a history of use stretching back 7,000 years. Deep blue [...]
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