Spinel

Spinel: an oxide of Magnesium, Aluminum, and other substituting elements such as Iron, Zinc, Manganese, and Chromium. It crystallizes in the Cubic System as octahedral crystals and is also found in massive form. It appears colorless and in various shades of pink, orange, red, purple, and violet. Density ranges from 3.58 to 3.61 g/cm³, with a common refractive index of 1.718–1.720.

(Photo: Rob Lavinsky, iRocks.com – CC-BY-SA-3.0/Wikimedia Commons, License CC BY-SA 3.0)

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