Delicatus Ice Granite (pegmatitic granite) 4 : 無料・フリー素材/写真
Delicatus Ice Granite (pegmatitic granite) 4 / James St. John
| ライセンス | クリエイティブ・コモンズ 表示 2.1 |
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| 説明 | "Delicatus Ice Granite" - pegmatitic granite attributed to Brazil.Igneous rocks form by the cooling & crystallization of hot, molten rock (magma & lava). If this happens at or near the land surface, or on the seafloor, they are extrusive igneous rocks. If this happens deep underground, they are intrusive igneous rocks. Most igneous rocks have a crystalline texture, but some are clastic, vesicular, frothy, or glassy.Granite is an very common intrusive igneous rock. Garden-variety granites are composed of quartz, potassium feldspar (K-feldspar), sodic plagioclase feldspar, hornblende amphibole, and mica. Granites have a felsic chemistry. Felsic igneous rocks are generally light-colored, have >65% silica (“silica” = SiO2 chemistry) (felsic has also been defined as >70% silica), are rich in potassium (K) & sodium (Na), and are dominated by the minerals quartz and K-feldspar.The cut-and-polished granite specimen shown above has a pegmatitic texture (many granites have a phaneritic texture, with crystals between 1 mm and 1 cm in size each). All or almost all of the crystals in a pegmatitic rock are >1 cm in size each. Pegmatitic granite usually forms by cooling of a relatively water-rich magma. Very slow cooling of magma can also result in a pegmatitic texture.Three principal minerals are present in this sample. The medium gray glassy material is quartz (SiO2 - silica/silicon dioxide). The whitish to whitish-gray material is potassium feldspar (KAlSi3O8 - potassium aluminosilicate). The thin black areas are biotite mica (K(Mg,Fe)3(AlSi3O10)(OH)2 - potassium magnesium iron hydroxy-aluminosilicate). The small, scattered red spots are garnet (click on the photo to zoom in & look around). |
| 撮影日 | 2017-06-29 16:23:18 |
| 撮影者 | James St. John |
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