{"id":1087,"date":"2014-08-04T20:07:29","date_gmt":"2014-08-04T20:07:29","guid":{"rendered":"https:\/\/waltonsons.com\/wp\/?page_id=1087"},"modified":"2014-10-31T05:15:14","modified_gmt":"2014-10-31T05:15:14","slug":"igneous-rock","status":"publish","type":"page","link":"https:\/\/waltonsons.com\/?page_id=1087","title":{"rendered":"IGNEOUS ROCK"},"content":{"rendered":"
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Shield Volcano: Mt Hood, OR.
Elsa B Walton<\/i><\/figcaption><\/figure>\n

Of the three classes of rock, igneous rock<\/i> is the most plentiful.\u00a0 Igneous rock forms after a volcano explosion.\u00a0 Mt. Hood in OR has the classic shape of a shield volcano.\u00a0 The Latin word, ignis<\/i>, means fire and igneous rock forms through the cooling and solidification of magma<\/i> or lava<\/i>, a hot molten or partially molten rock material.<\/p>\n

Magma is a silicate liquid generated by partial melting of the upper mantle or the lower crust. Different environments of formation, and the cooling rates associated with these, create very different textures and define the two major groupings within igneous rocks: Volcanic<\/i> or Plutonic<\/i>.<\/p>\n

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Half Dome, Yosemite, CA a granite monolith.
John Sullivan en.wikipedia.org\/wiki\/Granite<\/figcaption><\/figure>\n

Volcanic or extrusive rocks result from magma reaching the surface forming minerals such as pumice<\/i> or basalt<\/i>. \u00a0Plutonic or intrusive rocks result when magma cools and crystalizes slowly within the Earth\u2019s crust.\u00a0 A common example of this type is granite<\/i>.\u00a0 An example of a granite monolith is Half Dome in Yosemite, CA.<\/p>\n

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VOLCANIC ROCKS<\/b><\/p>\n

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Pumice Castle is solidified pyroclastic
material that was in a vent when
Mt Mazama (of Crater Lake) erupted.
Elsa B Walton<\/i><\/figcaption><\/figure>\n

Volcanic rocks form when magma rises to the surface and erupt, either as lava or pyroclastic material<\/i> forming minerals such as pumice<\/i> or basalt<\/i>.\u00a0 The rate of cooling of the magma is rapid, and crystal growth is inhibited. Such rocks are termed extrusive rocks<\/i>.\u00a0 An example is “Pumice Castle” made of pumice that hardened in the vent of Mt. Mazama at Crater Lake in OR.\u00a0 Volcanic rocks are characteristically fine-grained.\u00a0 Their texture is classified as \u201caphanitic<\/i>\u201d rock<\/i>.\u00a0 Volcanic rocks often exhibit structures caused by their eruption, e.g. flow band<\/i>ing (formed by shearing of the lava as it flows), and vesicles<\/i> (open cavities that represent escaped gasses).\u00a0 In order of composition from mafic<\/i> (magnesium rich) to felsic<\/i> (silica rich), volcanic rocks include basalt<\/i>, andesite<\/i>, dacite<\/i>, and rhyolite<\/i>.<\/p>\n

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PLUTONIC ROCKS<\/b><\/p>\n

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\"diorite_auckland\"
Diorite has phaneritic texture.
www.flexiblelearning.auckland.ac.nz<\/i><\/figcaption><\/figure>\n

Plutonic rocks<\/i> result when magma cools and crystalizes slowly within the Earth\u2019s crust. \u00a0Such rocks are termed intrusive rocks<\/i>.\u00a0 The name \u201cplutonic\u201d refers to Pluto, Roman god of the underworld.\u00a0 Plutonic rock is made of tightly packed mineral grains, which means it has phaneritic texture.<\/i>\u00a0 The grains are roughly equal size, meaning that it has equigranular<\/i> or granular texture. A common example of this type is granite<\/i>.\u00a0 Shown here is a good example of phaneritic texture in diorite, the plutonic equivilent of andesite.<\/p>\n

The environment of formation produces characteristic textures in igneous rocks, which aid in their identification. There are four types of igneous rock textures.<\/p>\n