(also plagioclase feldspar)
A form of feldspar consisting of aluminosilicates of sodium and/or calcium, common in igneous rocks and typically white.
- Aligned igneous minerals of euhedral potassium feldspar, plagioclase, biotite and hornblende in an undeformed quartz matrix define a magmatic foliation.
- All monazite grains are located in the rock matrix, which consists of quartz, muscovite, biotite, epidote, chlorite, plagioclase, potassium feldspar and garnet with a granoblastic texture.
- Coexisting MI phases in these rocks include garnet, plagioclase, quartz, tourmaline and fluorite.
Mid 19th century: from plagio- 'oblique' + Greek klasis 'cleavage' (because originally characterized as having two cleavages at an oblique angle).
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