essential mineral A primary mineral whose presence in an igneous rock is essential to defining the root name of that rock. For example, plagioclase and the pyroxene augite are essential to defining the root name ‘gabbro’ and hence are essential minerals. Where a primary mineral is present but is not essential to the naming of the rock it is termed an ‘accessory mineral’.
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essential , es·sen·tial / iˈsenshəl/ • adj. 1. absolutely necessary; extremely important: it is essential to keep up-to-date records. ∎ fundamental or central to… Arenaceous , arenaceous Sandy, or sand-like in appearance or texture. The term is applied to clastic sedimentary rocks with a grain size of 0.0625–2.00 mm. Three… Norite , norite A coarse-grained, basic igneous rock consisting of essential plagioclase feldspar, orthopyroxene (hypersthene or bronzite), and clinopyroxene… Iron Ores , Rocks Rocks are composed of minerals, which are natural inorganic (nonliving) substances with specific chemical compositions and structures. A rock m… Igneous Rocks , Igneous rocks are formed by the cooling and hardening of molten magma. The word igneous comes from the Latin word igneus, meaning fire, and there are… Metamorphic Rocks , Metamorphic rock is rock that has changed from one type of rock into another. The word metamorphic (from Greek) means “of changing form.” Metamorphic…
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