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diabase
Diabase or dolerite or microgabbro〔(【引用サイトリンク】 title=BGS Rock Classification Scheme - Dolerite (Synonymous with Microgabbro) )〕 is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine grained to aphanitic chilled margins which may contain tachylite (dark mafic glass). Diabase is the preferred name in North America, dolerite is the preferred name in most of the rest of the world, where sometimes the name diabase is applied to altered dolerites, though many petrologists prefer the name microgabbro to avoid this confusion.
==Petrography==
Diabase normally has a fine, but visible texture of euhedral lath-shaped plagioclase crystals (62%) set in a finer matrix of clinopyroxene, typically augite (20–29%), with minor olivine (3% up to 12% in olivine diabase), magnetite (2%), and ilmenite (2%).〔Klein, Cornelus and Cornelius S. Hurlbut, Jr.(1986) ''Manual of Mineralogy'', Wiley, 20th ed., p. 483 ISBN 0-471-80580-7〕 Accessory and alteration minerals include hornblende, biotite, apatite, pyrrhotite, chalcopyrite, serpentine, chlorite, and calcite. The texture is termed ''diabasic'' and is typical of diabases. This ''diabasic'' texture is also termed ''interstitial''.〔Morehouse, W. W. (1959) ''The Study of Rocks in Thin Section'', Harper & Row, p. 160〕 The feldspar is high in anorthite (as opposed to albite), the calcium endmember of the plagioclase anorthite-albite solid solution series, most commonly labradorite.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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