Stalactites. Quartz stalactites hanging down from the ceiling of a cave. These stalactites are icicle-shaped deposits of silicon oxide. They form over thousands of years from quartz carried in the water flowing beneath the earth's surface. As this water slowly drips through the cave roof,the cold conditions cause the quartz to precipitate out,gradually building up a stalactite. Together,the many differently coloured varieties of quartz make up 12% of the volume of the earth's crust | |
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