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The individual crystals in an aphanitic igneous rock are not distinguishable to the naked eye. Examples of aphanitic igneous rock include basalt , andesite , and rhyolite . Glassy or vitreous textures occur during some volcanic eruptions when the lava is quenched so rapidly that crystallization cannot occur.
The name diorite (from Ancient Greek διορίζειν, "to distinguish") was first applied to the rock by René Just Haüy [10] on account of its characteristic, easily identifiable large crystals of hornblende. [4] Dioritoids form a family of rock types similar to diorite, such as monzodiorite, quartz diorite, or nepheline-bearing diorite ...
Diorite – Igneous rock type Napoleonite, also known as corsite – Variety of diorite with orbicular structure; Dunite – Ultramafic and ultrabasic rock from Earth's mantle which is made of the mineral olivine; Essexite – Igneous rock type; Foidolite – Igneous rock rich in feldspathoid minerals; Gabbro – Coarse-grained mafic intrusive rock
Napoleonite is a variety of diorite which is characterized by orbicular structure. The grey matrix of the stone has the normal appearance of a diorite, but contains many rounded lumps 1 or 2 inches in diameter, which show concentric zones of light and dark colors.
Also called Indianite. A mineral from the lime-rich end of the plagioclase group of minerals. Anorthites are usually silicates of calcium and aluminium occurring in some basic igneous rocks, typically those produced by the contact metamorphism of impure calcareous sediments. anticline An arched fold in which the layers usually dip away from the fold axis. Contrast syncline. aphanic Having the ...
The change in the particle size of the rock during the process of metamorphism is called recrystallization. For instance, the small calcite crystals in the sedimentary rock limestone and chalk change into larger crystals in the metamorphic rock marble. [12]
Based on their color index, rocks can be classified as melanocratic (higher color index), leucocratic (lower color index), or mesocratic (middle color index), as well as hololeucocratic and holomelanocratic (extremes to either side). [1] For example, leucocratic granite would be brighter and have a lower color index than regular granite. [1]
Fractional crystallization, or crystal fractionation, is one of the most important geochemical and physical processes operating within crust and mantle of a rocky planetary body, such as the Earth. It is important in the formation of igneous rocks because it is one of the main processes of magmatic differentiation . [ 1 ]