how is opal made because its for a school project thanks?

Answer 1

Opal is formed from a solution of silicon dioxide and water. As water runs down through the earth, it picks up silica from sandstone, and carries this silica-rich solution into cracks and voids , caused by natural faults or decomposing fossils. As the water evaporates, it leaves behind a silica deposit. This cycle repeats over very long periods of time, and eventually opal is formed. The solution is believed to have a rate of deposition of approximately one centimetre thickness in five million years at a depth of forty metres.

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Answer 2

GEOLOGICALLY, opal is formed from low-temperature hydrothermal solutions or when groundwater leaches silica from the soil, leaving it behind in cracks deep within the earth after accumulated groundwater has evaporated. Nearly all of the world's supply of precious opal comes from Australia, which is famous for its white and black precious opal. Hungarian opal comes from mines in the Czerwenitza area; fire opal, from Querétaro state in central Mexico. Within the U.S., opal has been found in Arizona, Oregon, Idaho, Nevada, and a few other states.

According to information from the U.S. Geological Survey, opal is brittle, heat sensitive, and breaks and scratches easily; some varieties "self-destruct" through the loss of water, resulting in fine cracks that extend over the surface until they intersect and cause the gem to crumble. This process, called crazing, is one of the reasons why opal has been called a bad-luck stone. On the Mohs Scale of Hardness, where talc is rated 1 and diamond ends the scale at 10, opal is rated 5–6. Nevertheless, opal is still a premier gemstone.

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