View source for Felsite

{{short description|Very fine-grained volcanic rock that sometimes contains larger crystals}}
[[Image:Pyrolusite dendritic on felsite.jpg|thumb|Felsite covered with [[Dendrite (crystal)|dendritic]] [[pyrolusite]]]]
[[File:White Ring-Dyke At Campa - geograph.org.uk - 1163355.jpg|thumb|[[Dike (geology)|Dike]] of felsite on [[Islay]] in Scotland]]
'''Felsite''' is a very fine-grained  [[volcanic rock]] that may or may not contain larger [[crystal]]s. Felsite is a field term for a light-colored rock that typically requires [[petrographic]] examination or chemical analysis for more precise definition. Color is generally white through light gray, or red to tan and may include any color except dark gray, green or black (the colors of [[trap rock]]).<ref> Klein, Cornelis and Hurlbut, Cornelius S. (1986), ''Manual of Mineralogy,'' Wiley, p. 484 {{ISBN|0-471-80580-7}} </ref> The mass of the rock consists of a fine-grained [[matrix (geology)|matrix]] of [[felsic]] materials, particularly [[quartz]], [[plagioclase]] and [[potassium feldspar]],<ref>{{Cite journal|last1=McDonnell|first1=S.|last2=Troll|first2=V. R.|last3=Emeleus|first3=C. H.|last4=Meighan|first4=I. G.|last5=Brock|first5=D.|last6=Gould|first6=R. J.|date=October 2004|title=Intrusive history of the Slieve Gullion ring dyke, Ireland: implications for the internal structure of silicic sub-caldera magma chambers|url=https://www.cambridge.org/core/product/identifier/S0026461X0005355X/type/journal_article|journal=Mineralogical Magazine|language=en|volume=68|issue=5|pages=725–738|doi=10.1180/0026461046850215|bibcode=2004MinM...68..725M |s2cid=140159457 |issn=0026-461X|url-access=subscription}}</ref> and may be termed a quartz felsite or [[quartz porphyry]] if the quartz phenocrysts are present.  This rock is typically of [[extrusive]] origin, formed by compaction of fine [[volcanic ash]], and may be found in association with [[obsidian]] and [[rhyolite]].  In some cases, it is sufficiently fine-grained for use in making [[stone tool]]s. Its fine texture and felsic components allow for good [[knapped]] pieces, much like working [[chert]], producing [[conchoidal fracture]].  

[[Dendrite (metal)|Dendritic]] manganese oxides such as [[pyrolusite]] or iron oxides such as [[limonite]] may precipitate along rock crevices, giving some rock chunk surfaces multicolored or arborescent patterned textures.

==References==
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{{Rock type}}
[[Category:Igneous petrology]]
[[Category:Volcanic rocks]]

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{{Volcanoes}}