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Trachyte – Extrusive igneous rock – A silica-undersaturated volcanic rock; essentially a feldspathoid-bearing rhyolite; Troctolite – Igneous rock – A plutonic ultramafic rock containing olivine, pyroxene and plagioclase; Trondhjemite – Light-colored intrusive igneous rock – A form of tonalite where plagioclase-group feldspar is ...
Igneous rocks include rocks that have solidified from a melt either below the surface of a planet or natural satellite as intrusives or on the surface as extrusives or volcanic eruptions. The main article for this category is Igneous rock .
Grain size in igneous rocks results from cooling time so porphyritic rocks are created when the magma has two distinct phases of cooling. [18] Igneous rocks are classified on the basis of texture and composition. Texture refers to the size, shape, and arrangement of the mineral grains or crystals of which the rock is composed. [citation needed]
Color index, as a geological term, is a measure of the ratio between generally dark mafic minerals and generally light felsic minerals in an igneous rock. [ 1 ] [ 2 ] The color index of an igneous rock is the volume percentage of mafic minerals in the rock, excluding minerals generally regarded as "colorless" such as apatite , muscovite ...
Trachyte (/ ˈ t r eɪ k aɪ t, ˈ t r æ k-/) is an extrusive igneous rock composed mostly of alkali feldspar. It is usually light-colored and aphanitic (fine-grained), with minor amounts of mafic minerals, [1] and is formed by the rapid cooling of lava (or shallow intrusions) enriched with silica and alkali metals. [2] [3] [4] It is the ...
Nelsonite is an igneous rock primarily constituted of ilmenite and apatite, with anatase, chlorite, phosphosiderite, talc and/or wavellite appearing as minor components. Rocks are equigranular with a grain size around 2 – 3 mm. [ 2 ] The black ilmenite is slightly magnetic while the whitish apatite is not.
Mineralogical composition of igneous rocks with decreasing silica (SiO 2) content. The rock names for volcanic/extrusive and plutonic/intrusive rocks are written above. Notice that this is a rough way to determine a rock name: the exact difference between the given igneous rocks does not only depend on silica content. Date: March 2009: Source ...
Category: Igneous rocks by type. 9 languages. Беларуская (тарашкевіца) Bosanski; ... Intrusive rocks (3 C, 1 P) V. Volcanic rocks (8 C, 68 P)