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28_0d277ca2b0d8b8cd79fb9cfa322f77e1
2005-05-26 11:01:52

Diorite is a grey to dark grey intermediate intrusive igneous rock composed principally of plagioclase feldspar (typically andesine), hornblende, and/or pyroxene. Varieties deficient in hornblende and other dark minerals are called leucodiorite. It is often described as "salt and pepper" when composed largely of light-colored minerals randomly interspersed with dark minerals. When olivine and more iron-rich augite are present, the rock grades into ferrodiorite, which is transitional to...

28_30e95d7bc9a84ffe78f930c8704eb5b2
2005-05-26 11:00:22

Gabbro is a dark, coarse-grained, intrusive igneous rock chemically equivalent to basalt. It is a plutonic rock, formed when molten magma is trapped beneath the Earth's surface and cools slowly into a hard, coarsely crystalline mass. It is dense, greenish or dark-colored and contains varied percentages of plagioclase feldspar, pyroxene, amphibole, and olivine (called olivine gabbro when olivine is present in large quantities). Quartz gabbros are also known to occur and are probably derived...

28_c04342a5025a8ae7a0de88f6dc83278c
2005-05-25 11:55:01

Syenite is a coarse-grained intrusive igneous rock of the same general composition as granite but with the quartz either absent or present in relatively small amounts. The feldspars are alkaline in character and the dark mineral is usually hornblende. Soda-lime feldspars may be present in small quantities. The term syenite was originally applied to hornblende granite like that of Syene in Egypt, from which the name is derived. Syenite is not a common rock, some of the more important...

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Word of the Day
monteith
  • A large punch-bowl of the eighteenth century, usually of silver and with a movable rim, and decorated with flutings and a scalloped edge. It was also used for cooling and carrying wine-glasses.
  • A kind of cotton handkerchief having white spots on a colored ground, the spots being produced by a chemical which discharges the color.
This word is possibly named after Monteith (Monteigh), 'an eccentric 17th-century Scotsman who wore a cloak scalloped at the hem.'
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