# Lithophysa

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{{Short description|Felsic volcanic rock}}
thumb|A ''lithophysa'' from France
thumb|A collection of lithophysae "thundereggs"
A '''lithophysa''' (plural '''lithophysae''', from Greek ''lithos'' "stone" + ''phusa'' "bubble")<ref name = zianet>[http://www.zianet.com/geodekid/whatarel.htm What Are Lithophysae?]</ref> is a [felsic](/source/felsic) [volcanic](/source/volcanic) [rock](/source/Rock_(geology)) with a spherulitic structure and interior cavity with concentric chambers. Its outer shape is spherical or lenticular. They vary in size from very small up to twelve feet in diameter depending on the age of the magma chamber. These rocks are usually found within [obsidian](/source/obsidian) or [rhyolite](/source/rhyolite) lava flows.<ref>Roger Weller [http://skywalker.cochise.edu/wellerr/rocks/igrx/lithophysa1.htm Lithophysae cluster]</ref> Lavas low in [feldspar](/source/feldspar) minerals may produce a version known as [snowflake obsidian](/source/snowflake_obsidian).

These cavities  are believed to be caused by expanding gases in [tuff](/source/tuff)s and [rhyolitic](/source/rhyolitic) lavas before solidification.<ref name=zianet/> If the cavity becomes lined with [crystal](/source/crystal)s it may be referred to as a [geode](/source/geode) or if filled partially or fully with [agate](/source/agate), [jasper](/source/jasper) or [opal](/source/opal) it is called a [thunderegg](/source/thunderegg). The term [vug](/source/vug) is also used for similar cavities although the meaning of vug is usually restricted to cavities in rocks formed by the removal of material such as soluble minerals. These cavities usually contain layers of various colors (red, pink, gray, etc.) composed by crystals of quartz,<ref name=zianet/> [chalcedony](/source/chalcedony),<ref name=geow/> [hematite](/source/hematite), [fluorite](/source/fluorite)<ref>[http://www.mineralienatlas.de/lexikon/index.php/Lithophyse Mineralienatlas]</ref> and various colored oxides or other minerals.<ref name=zianet/>

thumb|Lithophysae from Richardson Ranch near Madras Oregon.<br/>
1, 2. Displaying typical plates and "sutures".<br/>
3, 4. A cluster with three spheroid centers.<br/>
5, 6. Example of slow fill structure layers with a large opal layer at the bottom. Expansion is controlled by where the water was located in the structure.<br/>
7. "Dimple" and "pimple" where expansion began on an inner shell.<br/>
8. Fortification agate

Lithophysae are one of the many forms of [silica](/source/silica) (SiO<sub>2</sub>),<ref name = geow>[http://www.geowiki.fr/index.php?title=Lithophyse Geowiki]</ref> as quartz,<ref name=zianet/> agate,<ref name=zianet/> opal,<ref name=zianet/> chalcedony, etc.  They can have an average diameter {{convert|5|-|20|cm}},<ref name=geow/> but can be much larger (for example, {{convert|10|–|12|ft|cm|order=flip}} at Silver Cliff in Colorado). Lithophysae are also related to the [spherulite](/source/spherulite)s found in obsidians on the [Italian](/source/Italy) island of [Lipari](/source/Lipari), in [Yellowstone National Park](/source/Yellowstone_National_Park), and other places.<ref>[https://books.google.com/books?id=3PqLMEetDfoC&dq=Lithophysae+lipari+yellowstone&pg=PA90 Geological Survey Bulletin, Ed. 136]</ref>

<gallery>
File:Spheroid-01.jpg|Spheroids form in high silica magmas
File:1.3-2019Spheroids 003-c1.jpg|Spheroid "trains" in obsidian
File:Snowflake obsidian - Utah.jpg|Snowflake obsidian
File:1.2-2014-02-29MarDaveGeodes 001cb.jpg|A partially "blown" spheroid pair in obsidian
File:01LithTrains.jpg|"Trains" of "blown" spheroids transformed to lithophysae
File:02inside1.jpg|"Blown" spheroid transformed to a lithophysa
File:02inside2.jpg|"Blown" spheroid transformed to a lithophysa
File:1.1-6Jun13-Drum-Oil 008.jpg|"Blown" spheroids transformed to lithophysae
</gallery>

==See also==
* [Lava balloon](/source/Lava_balloon)

== References ==
{{Commons}}
{{reflist}}

Category:Igneous petrology
Category:Mineralogy
Category:Volcanic rocks
Category:Volcanology

{{igneous-petrology-stub}}

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Adapted from the Wikipedia article [Lithophysa](https://en.wikipedia.org/wiki/Lithophysa) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Lithophysa?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.