Plagioclase Feldspar
Image: <a rel="nofollow" class="external text" href="https://www.flickr.com/people/12584677@N06">Leo-setä</a> (CC BY 2.0)
Mineral NamePlagioclase Feldspar
Chemical Formula(Na,Ca)Al(Si,Al)Si2O8
Mohs Hardness6
Crystal Systemtriclinic
Lustervitreous
Streak Colorwhite
CleavageTwo perfect cleavages, nearly at 90 degrees (86° and 94°)
Fractureconchoidal to uneven
Specific Gravity2.68
Colorswhite, grey, colorless
Transparencytransparent to translucent
Type LocalityUbiquitous, found worldwide in igneous, metamorphic, and some sedimentary rocks.
Mineral GroupSilicates
Usesindustrial, construction, gemstone
Associated Mineralspyroxene, amphibole, chlorite, epidote, opaque minerals
Raritycommon
Description
This microscopic image, taken under polarized light, displays a large grain of plagioclase feldspar characterized by distinct polysynthetic twinning, appearing as alternating light and dark bands. Adjacent to it is a brightly colored, irregularly shaped mineral, likely a mafic mineral undergoing alteration.
Geological Context
Plagioclase is a primary rock-forming mineral found in a wide range of igneous rocks, from felsic to mafic, and is also common in many metamorphic rocks. Its presence indicates crystallization from magma or recrystallization under specific pressure-temperature conditions.
