Geology glossary Minettes are a variety of igneous rock with phenocrysts of biotite, and with or without phenocrysts of hornblende, augite with a high diopside content, and olivine.

How is a Lamprophyre formed?

Distribution. Lamprophyres are usually associated with voluminous granodiorite intrusive episodes. They occur as marginal facies to some granites, though usually as dikes and sills marginal to and crosscutting the granites and diorites. In other districts where granites are abundant no rocks of this class are known.

Where is carbonatite found?

Overall, 527 carbonatite localities are known on Earth, and they are found on all continents and also on oceanic islands. Most of the carbonatites are shallow intrusive bodies of calcite-rich igneous rocks in form of volcanic necks, dykes, and cone-sheets.

What is Panidiomorphic texture?

Panidiomorphic refers to a texture in which, theoretically all the component mineral grains are subhedral. Allotriomorphic refers to a texture in which all the component mineral grains are anhedral.

What type of rock is Lamprophyre?

lamprophyre, any of a group of dark gray to black intrusive igneous rocks that generally occur as dikes (tabular bodies inserted in fissures).

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22 related questions found

Where do kimberlites form?

Kimberlite occurs in the Earth's crust in vertical structures known as kimberlite pipes, as well as igneous dykes. Kimberlite also occurs as horizontal sills. Kimberlite pipes are the most important source of mined diamonds today. The consensus on kimberlites is that they are formed deep within the mantle.

Is Lamprophyre a hypabyssal rock?

CONCLUSION  Lamprophyres are melanocratic ,porphyritic, hypabyssal rocks.  The lamprophyres commonly consists of alkali rich calc-alkali to ultramafic minerals. ... Although they have been reported from some younger alkaline complexes also.

What is Panidiomorphic?

/ (pæˌnɪdɪəʊˈmɔːfɪk) / adjective. (of igneous rocks) having well-developed crystals.

What is Holohyaline texture?

A term applied to igneous rocks that have a glassy texture. Holohyaline rocks were generally cooled rapidly, which inhibits growth rate and nucleation of crystals. A few tiny crystals, called microlites, may be present.

What is a Holocrystalline definition?

: completely crystalline : made up wholly of crystals or crystalline particles —used of a rock (as granite)

What is carbonatite used for?

Uses. Carbonatite is the principal source of niobium which comes from the mineral pyrochlore (mined in Brazil and Canada — Araxá, Tapira, and St. Honoré mines). Carbonatites also contain lots or rare earth elements.

What type of rock is carbonatite?

Carbonatites are a relatively rare type of igneous rock composed of greater than 50 vol % primary carbonate minerals, primarily calcite and/or dolomite, and contain the highest concentrations of REEs of any igneous rocks.

What are carbonates in geology?

Carbonate rocks are a class of sedimentary rocks composed primarily of carbonate minerals. The two major types are limestone, which is composed of calcite or aragonite (different crystal forms of CaCO₃), and dolomite rock (also known as dolostone), which is composed of mineral dolomite (CaMg(CO₃)₂).

What is Khondalite rocks?

Khondalite is a foliated metamorphic rock. In India, it is also called Bezwada Gneiss and Kailasa Gneiss. It was named after the Khond tribe of Odisha and Andhra Pradesh because well-formed examples of the rock were found in the inhabited hills of these regions of eastern India.

What is Poikilitic texture in geology?

Poikilitic texture refers to crystals, typically phenocrysts, in an igneous rock which contain small grains of other minerals. In igneous rocks Poikilitic texture is widely used to determine order of crystallization; if one mineral is enclosed by another then the enclosed grain must have been the first to crystallize.

What is Ophitic texture in geology?

Ophitic texture is the association of lath-shaped euhedral crystals of plagioclase, grouped radially or in an irregular mesh, with surrounding or interstitial large anhedral crystals of pyroxene; it is characteristic of the common rock type known as diabase.

Is Obsidian a Holohyaline?

Obsidian is a holohyaline rock.

Is quartz an Aphanitic?

Aphanites are commonly porphyritic, having large crystals embedded in the fine groundmass, or matrix. ... They consist essentially of very small crystals of minerals such as plagioclase feldspar, with hornblende or augite, and may contain also biotite, quartz, and orthoclase.

How Myrmekite is formed?

Myrmekite, irregular, wormy penetration by quartz in plagioclase feldspar; these wartlike, wormlike, or fingerlike bodies may develop during the late stages of crystallization of igneous rocks if the two minerals (quartz and feldspar) grow simultaneously in the presence of a volatile phase.

What is Euhedral in geology?

Euhedral crystals (also known as idiomorphic or automorphic crystals) are those that are well-formed, with sharp, easily recognised faces. ... As magma cools, the crystals grow and eventually touch each other, preventing crystal faces from forming properly or at all.

What is Allotriomorphic?

: marked by a form different from the normal or expected because of development in special circumstances —used especially of mineral grains of igneous rocks whose mutual growths have prevented the assumption of outward crystal form —contrasted with idiomorphic.

What does a porphyritic rock look like?

Porphyritic - This texture describes a rock that has well-formed crystals visible to the naked eye, called phenocrysts, set in a very fine grained or glassy matrix, called the groundmass. ... This texture is characteristic of most volcanic rocks.

What is Hypabyssal igneous rock?

A subvolcanic rock, also known as a hypabyssal rock, is an intrusive igneous rock that is emplaced at depths less than 2 km (1.2 mi) within the crust, and has intermediate grain size and often porphyritic texture between that of volcanic rocks and plutonic rocks.

How do S type granites form?

The interpretation of S-type granites are that they are sourced from the partial melting of sedimentary rocks (supracrustal) that have been through one or more cycles of weathering. Evidence for this include aluminium and silica enrichment, caused by the weathering process of the source rock.

Where do you find peridotite?

Peridotite is the dominant rock of the upper part of Earth's mantle. The compositions of peridotite nodules found in certain basalts and diamond pipes (kimberlites) are of special interest, because they provide samples of Earth's mantle brought up from depths ranging from about 30 km to 200 km or more.