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serpentine


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A group of minerals belonging to the 1:1 group of phyllosilicates (sheet silicates) with the composition Mg6[Si4O10](OH)8 and including the minerals chrysotile (the asbestiform variety), lizardite, and antigorite; sp. gr. 2.55–2.60; hardness 2.0–3.5; monoclinic; chrysotile is fibrous whereas lizardite and antigorite occur as flat tabular crystals or massive; various shades of green, also brown, grey-white, or yellow; greasy to waxy lustre, occasionally silky; formed from altered olivine and orthopyroxene. It results from the alteration of ultramafic (see ultrabasic) rocks either by hydrothermal action at a late stage or by alteration during metamorphism, chrysotile forming first and then altering to antigorite; it is a constituent of ophicalcites, a serpentine-calcite rock derived from the dedolomitization (see dedolomite) of a siliceous dolomite. It is used extensively as a facing stone and for ornament; chrysotile has been used as a source of commercial asbestos in Thetford, Canada. Lizardite occurs on the Lizard Peninsula, Cornwall, UK.

Subjects: Earth Sciences and Geography.


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