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A crystal of tourmaline is built up of units consisting of a six-member silica ring that binds above to a large cation, such as sodium. The ring binds below to a layer of metal ions and hydroxyls or halogens, which structurally resembles a fragment of kaolin. This in turn binds to three triangular borate ions.
Elbaite, a sodium, lithium, aluminium boro-silicate, with the chemical composition Na(Li 1.5 Al 1.5)Al 6 Si 6 O 18 (BO 3) 3 (OH) 4, [4] is a mineral species belonging to the six-member ring cyclosilicate tourmaline group.
Group of precious and semiprecious stones—both uncut and faceted—including (clockwise from top left) diamond, uncut synthetic sapphire, ruby, uncut emerald, and amethyst crystal cluster. A gemstone (also called a fine gem , jewel , precious stone , semiprecious stone , or simply gem ) is a piece of mineral crystal which, when cut or ...
Amazonite, also known as amazonstone, [4] is a green tectosilicate mineral, a variety of the potassium feldspar called microcline. [4] [5] [6] Its chemical formula is KAlSi 3 O 8, [1] [7] which is polymorphic to orthoclase.
Structurally, it is a hexagonal crystal with a brilliant reflecting green colour. The emerald is highly polished and is found in metamorphic rocks , granites , and mica schist. Many of the finest specimens have been found in Muzo , Bogota , South America but the ancients obtained the stone from Egypt and India.
A crystal's crystallographic forms are sets of possible faces of the crystal that are related by one of the symmetries of the crystal. For example, crystals of galena often take the shape of cubes, and the six faces of the cube belong to a crystallographic form that displays one of the symmetries of the isometric crystal system. Galena also ...
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