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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 result is a natural amorphous glass ...
Close-up of granite, a phanerite rock, from Yosemite National Park in California, U.S. Phaneritic diorite from Massachusetts. A phanerite [1] is an igneous rock whose microstructure is made up of crystals large enough to be distinguished with the unaided human eye. In contrast, the crystals in an aphanitic rock are
In geology, texture or rock microstructure [1] refers to the relationship between the materials of which a rock is composed. [2] The broadest textural classes are crystalline (in which the components are intergrown and interlocking crystals), fragmental (in which there is an accumulation of fragments by some physical process), aphanitic (in which crystals are not visible to the unaided eye ...
For textural classification, igneous rocks that have crystals large enough to be seen by the naked eye are called phaneritic; those with crystals too small to be seen are called aphanitic. Generally speaking, phaneritic implies an intrusive origin or plutonic, indicating slow cooling; aphanitic are extrusive or volcanic, indicating rapid cooling.
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An aphanitic volcanic sand grain, with fine-grained groundmass, as seen through a petrographic microscope Aphanites (adj. aphanitic ; from Ancient Greek αφανης (aphanḗs) 'invisible') are igneous rocks that are so fine-grained that their component mineral crystals are not visible to the naked eye [ 2 ] (in contrast to phanerites , in ...
Rhyolite (/ ˈ r aɪ. ə l aɪ t / RY-ə-lyte) [1] [2] [3] [4] is the most silica-rich of volcanic rocks.It is generally glassy or fine-grained in texture, but may be ...
Vesicular texture in volcanic rock from Tenerife Vesicular olivine basalt from La Palma. Vesicular texture is a volcanic rock texture characterized by a rock being pitted with many cavities (known as vesicles) at its surface and inside.