Miarolitic cavities (or ''miarolitic texture'') are typically crystal-lined irregular cavities or
vug
A vug, vugh, or vugg (
) is a small- to medium-sized cavity inside rock. It may be formed through a variety of processes. Most commonly, cracks and fissures opened by tectonic activity (folding and faulting) are partially filled by quartz, ...
s most commonly found in
granitic
A granitoid is a generic term for a diverse category of coarse-grained igneous rocks that consist predominantly of quartz, plagioclase, and alkali feldspar. Granitoids range from plagioclase-rich tonalites to alkali-rich syenites and from quartz- ...
pegmatites, and also in a variety of
igneous rocks. The central portions of pegmatites are often miarolitic as the pegmatite
dike
Dyke (UK) or dike (US) may refer to:
General uses
* Dyke (slang), a slang word meaning "lesbian"
* Dike (geology), a subvertical sheet-like intrusion of magma or sediment
* Dike (mythology), ''Dikē'', the Greek goddess of moral justice
* Dikes ...
crystallizes from the outside walls toward the center. The
volatile portion of the
magma
Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural sa ...
is gradually excluded from the forming crystal phases until it becomes trapped within the body and forms the cavities which often contain
mineral
In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...
s of elements incompatible with the typical
silicate granitic mineralogy.
The miarolitic cavities and miarolitic pegmatites are sources of rare and unusual minerals containing elements not found in abundance in normal igneous rocks. Minerals containing lithium, rubidium, beryllium, boron, niobium, tantalum, tin, bismuth, fluorine and other elements can be found.
The term ''miarolitic'' comes from the
Italian
Italian(s) may refer to:
* Anything of, from, or related to the people of Italy over the centuries
** Italians, an ethnic group or simply a citizen of the Italian Republic or Italian Kingdom
** Italian language, a Romance language
*** Regional Ita ...
''miarole'' in reference to the mineral-rich pegmatite region of Baveno and Cuasso al Monte in northern Italy.
References
PDFLondon, David, ''Formation of tourmaline-rich gem pockets in miarolitic pegmatites'' American Mineralogist, Volume 71, pages 396–405, 1986
Mineralogy
Petrology
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