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
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)