JOHN WALSH / SCIENCE PHOTO LIBRARY JOHN WALSH / SCIENCE PHOTO LIBRARY
Macrophotograph of sapphire or corundum. The mineral corundum or aluminium oxide occurs as well developed hexagonal crystals which may be arranged in prismatic, rhombohedral, pyramidal or tabular manner. Corundum is valued as an abrasive (e.g. emery), & as a gemstone. Gemstones are fragments of certain minerals, artificially polished, which are hard, relatively free from cleavage & occur as transparent crystals. Transparent corundum when tinted blue, as here, is called sapphire. When coloured red it is called ruby. Magnification: x10 (6x4cm size).
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