Plutonic rocks

Plutonic rocks as the stratified division of the crystalline or hypo gene formations, and have stated that they differ from the volcanic rocks, not only by their more crystalline texture, but also by the absence of tuffs and breccia’s, which are the products of eruptions at the earth’s surface, whether thrown up into the air or the sea. They differ also by the absence of pores or cellular cavities, to which the expansion of the entangled gases gives rise in ordinary lava, never being scoriaceous or amygdaloidal, and never forming a porphyry with an uncrystalline base, nor alternating with tuffs. From these and other peculiarities it has been inferred that the granites have been formed at considerable depths in the earth, and have cooled and crystallized slowly under great pressure, where the contained gases could not expand. The volcanic rocks, on the contrary, although they also have risen up from below, have cooled from a melted state more rapidly upon or near the surface.The Plutonic rocks may be treated of next in order, as they are most nearly allied to the volcanic class already considered. Types of plutonic rocks: Common plutonic rocks: Plutonic rocks are igneous rocks that are formed deep under the Earth's surface and have a coarse grain size. They can be separated into acidic, basic and ultrabasic types, according to their mineral and chemical composition. Acidic plutonic rocks: Granite: the most common igneous plutonic rock. Contains essential quartz, plagioclase and alkali feldspar, usually with hornblende and/or biotite and/or muscovite. Granodiorite:a plutonic rock with essential quartz and plagioclase, with lesser amounts of alkali feldspar and small amountsof hornblende and biotite. Tonalite:a plutonic rock with essential quartz and sodic plagioclase, usually with lesser biotite and amphibole. Aplite:fine-grained, composed mostly of quartz and feldspars. Pegmatite: a very coarse-grained, usually plutonic granitic rock. Basic plutonic rocks: Diorite: a plutonic rock composed of sodic plagioclase, commonly hornblende, and/or biotite or Augite. Gabbro: a coarse-grained plutonic rock with essential calcic plagioclase, pyroxene and opaque minerals, and/or hornblende or olivine. The plutonic equivalent of basalt. Monzonite: a plutonic rock with equal amounts of plagioclase and alkali feldspar, along with lesser amphibole and/or pyroxene. Syenite: a plutonic rock composed mainly of alkali feldspar, with subordinate sodic plagioclase, biotite, pyroxene, and amphibole. Ultrabasic plutonic rocks: Anorthosite:a plutonic rock with mostly calcic plagioclase and small amounts of pyroxene. Dunite:a plutonic rock composed mostly of olivine. Clinopyroxenite:a plutonic rock composed mostly of clinopyroxene. Harzburgite: a plutonic rock composed of essential olivine and orthopyroxene. Hornblendite: a plutonic rock composed mostly of hornblende. Lherzolite: a plutonic rock composed largely of olivine, along with lesser clinopyroxene and orthopyroxene, and sometimes spinel. Orthopyroxenite: a plutonic rock composed mostly of orthopyroxene. Peridotite: a plutonic rock composed of olivine with lesser pyroxene and/or amphibole. Pyroxenite: a plutonic rock composed largely of pyroxene.