How are rubies formed?

After diamonds, the ruby is the gemstone that occurs the least frequently in nature. The ruby is a variety of the mineral corundum. Just like most gemstones, rubies formed million of years ago at a depth of 5 to 40 kilometres under the Earth's crust. The cooling of magma forms crystals, which acquire intense colours due to the presence of metals. The ruby owes its typical red colour to the presence of chromium.

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