A gemstone or gem also called a precious or semi-precious stone or jewel is a piece of mineral which in cut and polished form is used to make jewelry or other adornments.However certain rocks, such as la pis lazuli and organic materials such as amber or jet are not minerals, but are still used for jewelry and are therefore often considered to be gemstones as well.
Wednesday, April 27, 2011
OPAL
Opal is an amorphous form of silica related to quartz, a mineraloid form, not a mineral. 3% to 21% of the total weight is water, but the content is usually between 6% to 10%. It is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock, being most commonly found with limonite, sandstone, rhyolite, marl and basalt. 97% of opal is produced in Australia and is its national gemstone.[4
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