A practical guide to rock microstructure. (2008): Principles of Metamorphic Petrology. Igneous and metamorphic rocks under the microscope: classification, textures, microstructures and mineral preferred-orientations. Principles of igneous and metamorphic petrology. An introduction to the rock-forming minerals (p. Interference colors: Low (gray-yellow).Form Rarely euhedral, usually as small rounded crystals.Other occurrences are as masses adjacent to ultramafic intrusives, associated with lamprophyre dikes and as large crystals in pegmatites. It also occurs in low silica igneous syenite and nepheline syenite intrusives. Corundum occurs as a mineral in mica schist, gneiss, and some marbles in metamorphic terranes. All other colors are called sapphire, e.g., 'green sapphire' for a green specimen. Transparent specimens are used as gems, called ruby if red and padparadscha if pink-orange. It is one of the naturally clear transparent materials, but can have different colors when impurities are present. Known by many names in ancient times: adamant, sapphire, ruby, hyacinthos, asteria.Ĭorundum is a crystalline form of aluminium oxide (Al 2O 3). Richard Kirwan used the current spelling 'corundum' in 1794.

The country earned around half a billion dollars through the export of gems, diamonds and other jewelry last year, the local gems and jewelry industry body has reported.Named 'corinvindum' in 1725 by John Woodward and derived from the Sanskrit, kuruvinda ('Ruby'). Ratnapura is known as the gem capital of the South Asian country, which is a leading exporter of sapphires and other precious gems. The stone was found in the gem-rich Ratnapura area where local people had previously found the world's largest star sapphire cluster in a backyard by accident. A group of Buddhist monks chanted blessings for the gemstone before it was unveiled. The sapphire was put on display at the home of one of the gem pit owners in Horana, 65 kilometres (40 miles) south of Colombo. International organizations are yet to certify the precious stone. Local gemologists, who have examined the sapphire, said it was one of the rarest gems in the world as it weighed more than 300 kilograms. Sri Lankan authorities on Sunday put on show what they said was the world's largest natural corundum blue sapphire, weighing 310 kilograms, which was found in a gem pit about three months ago.

Corundum blue