Editing Aphanite

{{short description|Igneous rock composed of very small crystals invisible to the naked eye}}
[[File:VolcanicBombMojaveDesert.JPG|thumb|The smooth texture of this [[basalt]]ic [[volcanic bomb]] is aphanitic.]]
[[File:Classification extrusive rocks EN.svg|thumb|upright=1.3|[[IUGS]] classification of aphanitic [[extrusive rock|extrusive]] [[igneous rock]]s according to their relative alkali (Na<sub>2</sub>O + K<sub>2</sub>O) and silica (SiO<sub>2</sub>) weight contents. Blue area is roughly where alkaline rocks plot; yellow area where subalkaline rocks plot.<ref>{{cite book |editor-last=Le Maitre |editor-first=R. W. |year=1989 |title=A classification of igneous rocks and glossary of terms |publisher=[[Wiley-Blackwell|Blackwell Science]] |location=Oxford}}</ref>]]
[[File:LvMS-Lvv.jpg|thumb|An aphanitic volcanic sand grain, with fine-grained [[matrix (geology)|groundmass]], as seen through a [[petrographic microscope]]]]

'''Aphanites''' (adj. ''aphanitic''; {{etymology|grc|''αφανης'' (aphanḗs)|invisible}}) are [[igneous rock]]s that are so [[grain size|fine-grained]] that their component [[mineral]] [[crystal]]s are not visible to the [[naked eye]]<ref name="EB1911">{{EB1911|inline=y|wstitle=Aphanite|volume=2|page=163}}</ref> (in contrast to [[phanerite]]s, in which the crystals are visible to the unaided eye). This [[texture (geology)|geological texture]] results from rapid cooling in [[volcanic rock|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.<ref>{{cite book |author=Bates and Jackson |year=1984 |title=Dictionary of Geological Terms |edition=3rd |publisher=[[American Geological Institute]]}}</ref>

Aphanites are commonly [[porphyritic]], having large crystals embedded in the fine groundmass, or [[matrix (geology)|matrix]].  The larger [[inclusion (mineral)|inclusions]] are called [[phenocryst]]s. 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]].<ref name="EB1911"/>

==Common rocks that can be aphanitic==
* [[Andesite]]
* [[Basalt]]
* [[Basanite]]
* [[Dacite]]
* [[Felsite]]
* [[Phonolite]]
* [[Rhyolite]]
* [[Trachyte]]

==References==
<references/>
{{Rock type}}
[[Category:Aphanitic rocks]]
[[Category:Igneous petrology]]
[[Category:Volcanic rocks]]
[[Category:Subvolcanic rocks]]


{{igneous-rock-stub}}