Aphanite

The smooth texture of this basaltic volcanic bomb is aphanitic.

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 which the crystals are visible to the unaided eye), however visible using magnification (in contrast to Cryptocrystallines, in which the crystals are not visible even under microscope). This geological texture results from rapid cooling in volcanic or hypabyssal (shallow subsurface) environments. As a rule, the texture of these rocks is not the same as that of volcanic glass (e.g., obsidian), with volcanic glass being non-crystalline (amorphous), and having a glass-like appearance.^[3]

Aphanites are commonly porphyritic, having large crystals embedded in the fine groundmass, or matrix. The larger inclusions are called phenocrysts. They consist essentially of very small crystals of minerals such as plagioclase feldspar, with hornblende or augite, and may contain also biotite, quartz, and orthoclase.^[2]

Common rocks that can be aphanitic

References

↑ Le Maitre, R. W., ed. (1989). A classification of igneous rocks and glossary of terms. Oxford: Blackwell Science.
1 2 One or more of the preceding sentences incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). "Aphanite". Encyclopædia Britannica. Vol. 2 (11th ed.). Cambridge University Press. p. 163.
↑ Bates and Jackson (1984). Dictionary of Geological Terms (3rd ed.). American Geological Institute.

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[1] Le Maitre, R. W., ed. (1989). A classification of igneous rocks and glossary of terms. Oxford: Blackwell Science.

[EB1911-2] 1 2 One or more of the preceding sentences incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). "Aphanite". Encyclopædia Britannica. Vol. 2 (11th ed.). Cambridge University Press. p. 163.

[3] Bates and Jackson (1984). Dictionary of Geological Terms (3rd ed.). American Geological Institute.

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v t e Types of rocks
Igneous rock	Andesite Icelandite Boninite Sanukite Anorthosite Aplite Basalt Alkali basalt Picrite basalt Basaltic trachyandesite Mugearite Shoshonite Basanite Blairmorite Carbonatite Natrocarbonatite Sovite Charnockite Enderbite Dacite Adakitic dacite Diabase Diorite Napoleonite Foidolite Ijolite Gabbro Troctolite Norite Hornblende gabbro Granite Alkali feldspar granite Monzogranite Granodiorite Granophyre Hornblendite Hyaloclastite Komatiite Lamproite Lamprophyre Monzonite Monzogabbro Essexite Nepheline syenite Nephelinite Obsidian Pegmatite Peridotite Wehrlite Dunite Harzburgite Lherzolite Kimberlite Phonolite Phonotephrite Pumice Pyroxenite Websterite Clinopyroxenite Orthopyroxenite Quartz diorite Quartz monzonite Quartzolite Rhyodacite Rhyolite Comendite Pantellerite Scoria Reticulite Shonkinite Sideromelane Syenite Tachylite Tephriphonolite Tephrite Tonalite Trondhjemite Trachyandesite Benmoreite Latite Trachybasalt Hawaiite Trachyte Tuff Ignimbrite
Sedimentary rock	Banded iron formation Breccia Chert Flint Coal Lignite Anthracite Conglomerate Diamictite Diatomite Dolomite Evaporite Geyserite Jaspillite Laterite Limestone Calcarenite Chalk Coquina Lumachelle Marl Oolite Travertine Tufa Wackestone Mudstone Argillite Claystone Shale Siltstone Oil shale Phosphorite Sandstone Arkose Greywacke Gritstone Itacolumite Sylvinite Tillite Turbidite Varve
Metamorphic rock	Amphibolite Blueschist Cataclasite Corundite Eclogite Gneiss Granulite Greenschist Hornfels Calcflinta Itabirite Litchfieldite Marble Migmatite Mylonite Metapelite Phyllite Pseudotachylite Quartzite Schist Serpentinite Skarn Slate Suevite Talc carbonate Soapstone Tectonite Whiteschist
Specific varieties	Adamellite Appinite Aphanite Borolanite Blue Granite Epidosite Felsite Flint Ganister Gossan Hyaloclastite Ijolite Jadeitite Jasperoid Kenyte Lapis lazuli Larvikite Litchfieldite Llanite Luxullianite Mangerite Novaculite Pyrolite Rapakivi granite Rhomb porphyry Rodingite Shonkinite Taconite Teschenite Theralite Unakite Variolite Wad

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Aphanite

Common rocks that can be aphanitic

See also

References