View source for Vug

{{Short description|Small to medium-sized cavity inside rock}}
{{Other uses}}
{{Use dmy dates|date=April 2022}}
[[File:Vug 5614.JPG|thumb|This vug in the [[Cascade Range]] is partially filled with [[quartz]] crystals.]]

A '''vug''', '''vugh''', or '''vugg''' ({{IPAc-en|'|v|ʌ|ɡ|}})<ref name="FreeDictionary">{{cite web |url=http://www.thefreedictionary.com/Vug |title=vug |work=[[The Free Dictionary]] |publisher=Farlex |access-date=2016-04-17 }}</ref> is a small- to medium-sized{{Quantify|date=April 2022}} cavity inside [[rock (geology)|rock]]. It may be formed through a variety of processes. Most commonly, cracks and [[fissure]]s opened by [[tectonics|tectonic]] activity ([[fold (geology)|folding]] and [[fault (geology)|faulting]]) are partially filled by [[quartz]], [[calcite]], and other secondary [[mineral]]s. Open spaces within [[breccia]]s formed by an ancient collapse are another important source of vugs.{{citation needed|date=January 2023}}

Vugs may also form when mineral [[crystal]]s or [[fossil]]s inside a [[matrix (geology)|rock matrix]] are later removed through [[erosion]] or [[solvation|dissolution]] processes, leaving behind irregular voids. The inner surfaces of such vugs are often coated with a crystal [[druse (geology)|druse]]. Fine crystals are often found in vugs where the open space allows the free development of external crystal form.

The term ''vug'' is not applied to veins and fissures that have become completely filled, but may be applied to any small cavities within such veins. [[Geode]]s are a vug-formed rock, although that term is usually reserved for more rounded crystal-lined cavities in [[sedimentary rock]]s and ancient [[lava]]s.<ref>[https://geology.buzz/threads/vug.79/ Geology Buzz: Vug]</ref>

The word ''vug'' was introduced to the English language by [[Cornwall|Cornish]] [[Mining|miners]], from the days when Cornwall was a major supplier of [[tin]].<ref name="auto">''The history of Cornwall, civil, military, religious, ...'' (Page 56), [[Richard Polwhele]] - 1816</ref> The [[Cornish language|Cornish]] word was {{lang|kw|vooga}}, which meant "cave".<ref name="auto"/>

== Images ==
<gallery widths="133" heights="130">
File:Conichalcite-Calcite-65643.jpg|A vug in a [[limonite]] matrix is the host for a layer of green botryoids of [[conichalcite]] and colorless, translucent rhombs of calcite
File:Azurite-Malachite-163967.jpg|Vug with rosettes of deep blue [[azurite]] on a field of malachite
File:Goosecreekite-Heulandite-Ca-Quartz-indi-41a.jpg|[[Goosecreekite]] with [[heulandite]]-Ca on quartz
File:Rosasite-rosa08a.jpg|Intergrown botryoids of blue-green [[rosasite]] inside the curve of a limonite vug
File:Epistilbite-indi-15a.jpg|Example of open space in a vug allowing the formation of crystallized minerals
File:Pyromorphite-t07-109a.jpg|Apple green [[pyromorphite]] cluster on limonite matrix
File:Wulfenite-181388.jpg|Vug in a limonitic matrix is the host for bi-pyramidal, brownish-red crystals of [[wulfenite]]
File:Groutite-tuc1048a.jpg|Crystallized [[groutite]] scattered about a hollow vug
File:Aurichalcite-Calcite-aur06a.jpg|In a vug of limonite are intergrown clusters of rhombohedral calcite with [[Inclusion (mineral)|inclusion]]s of fibrous [[aurichalcite]]
File:Epistilbite-Fluorapophyllite-Stellerite-indi-20a.jpg|[[Stellerite]], [[epistilbite]], and [[eluorapophyllite]] in a basaltic vug
File:Sulfur-tmix07-162b.jpg|Nestled in its matrix vug are five golden-yellow crystals of [[sulfur]]
File:Quartz-Chrysocolla-193915.jpg|In an open pocket in a matrix of limonite there is a cluster of deep robin's-egg blue [[chrysocolla]] with a covering of [[drusy]] quartz
</gallery>

==See also==
* [[Amygdule]]
* [[Rock microstructure]]
* [[Vesicular texture]]

==References==
<references/>

==External links==
*{{wiktionary-inline}}

[[Category:Petrology]]
[[Category:Geology terminology]]
[[Category:Cornish words and phrases]]