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Diorite

Chemical Process (Liquid-phase Growth) - Closed system under ground (Melt precipitation)

Definition

Igneous rocks with equigranular texture having mineral compositions as follows: Quartz in felsic minerals = 0-5 vol%, Plagioclase in feldspar = 90-100 vol%, and An in plagioclase < 50 %. Other characters summarized below are those of general diorites, and the rock type may be inferred but cannot be determined by mineral assemblages.

Mineral composition

Mafic minerals = 30-60 vol% (Neutral), Quartz in felsic minerals = 0-5 vol%, Plagioclase in feldspar = 90-100 vol%, An in plagioclase < 50 %

Chemical composition

SiO2 = 52-66 wt% (Neutral).

Texture

Equigranular texture composed of grains more than a few mm.

Required Geological Setting

Plutonic rocks

Occurrence

Rock forming minerals in diorite, felsic (acidic) plutonic rock formed from magma under ground. Diorite distributes in continents and island arcs associated with Granite batholiths and stocks.

Mineral Assemblages

Plagioclase (Oligoclase), Pyroxene, Magnesio-hornblende, (Quartz, K-feldspar)

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