crystals of hematite, crystals of microcline var. amazonite : Pikes Peak Granite, Teller Co., Colorado, USA — Photo: Parent Géry · CC BY-SA 3.0
Microcline
Also known as: Amazonstone (green var.).
The low-temperature potassium feldspar — common in granite and pegmatite, and the green variety called amazonite.
Intro adapted from Wikipedia (CC BY-SA).
Microcline is an IMA-recognized mineral species in the silicate class, with the chemical formula K(AlSi₃O₈).
It crystallizes in the triclinic crystal system (space group C-1). It is a member of the Feldspar structural group.
Key properties: Mohs hardness 6–6.5; specific gravity 2.54–2.57; typically green or white or pink or gray or brown; white streak; Vitreous, pearly on cleavage luster; optically biaxial.
IMA symbol Mcc, grandfathered status — known before the IMA’s founding, named in 1830.
Common in plutonic felsic rocks, as granites, granite pegmatites, syenites; in metamorphic rocks of the greenschist and amphibolite facies; in hydrothermal veins. A detrital component in sedimentary rocks and as authigenic overgrowths.
It is found associated with Quartz, sodic plagioclase, muscovite, biotite, \hornblende.".
Its name comes from the Greek for little and inclined, for the small deviation of the cleavage planes from 90±.
Collections: Everyday Minerals, Collector Favorites.