thumb|A lithophysa from France
thumb|A collection of lithophysae "thundereggs"
A lithophysa (plural lithophysae, from Greek lithos "stone" + phusa "bubble") is a felsic volcanic rock 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 or rhyolite lava flows. Lavas low in feldspar minerals may produce a version known as snowflake obsidian.
These cavities are believed to be caused by expanding gases in tuffs and rhyolitic lavas before solidification. and various colored oxides or other minerals. as quartz,
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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
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See also
- Lava balloon