According to its growth rings, the zircon crystal below took 200 million years to grow.

Researchers at the University of Western Ontario discovered these crystals in northern Ontario. For something so small – less than the width of a human hair – they are having a massive impact: their existence has prompted a re-examination of the expected result of subjecting crystals like this to heat and pressure deep under the Earth.
Ideas about how minerals and crystals respond to these conditions may now have to be re-visited. Amazing to think, though, that crystals can be dated in the same way as trees.
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