LAWRENCE LAWRY / SCIENCE PHOTO LIBRARY LAWRENCE LAWRY / SCIENCE PHOTO LIBRARY
Precious gemstones of ruby (red) and sapphire (blue), which are varieties of the mineral corundum (aluminium oxide). Gemstones are solid crystalline substances (minerals), formed by natural processes, which are prized by collectors and used in jewellery. Cut and polished stones utilize the refraction of light to enhance their appearance.
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