mineral

Plagioclase Feldspar

NaAlSi3O8 – CaAlSi2O8 (Sodium-Calcium Aluminum Silicates)

Hardness: 6.0 – 6.5 on Mohs scale; Color: White to gray; Luster: Vitreous to pearly; Crystal structure: Triclinic; Cleavage: Two distinct directions nearly at 90 degrees; Specific gravity: 2.6 – 2.8

Hardness: 6
Color: White to gray
Luster: Vitreous to pearly

Identified March 31, 2026More mineral →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed through the cooling and crystallization of igneous rocks (both intrusive and extrusive), as well as in metamorphic rocks. It is a primary constituent of Earth's crust across various geological ages.

Uses & applications

Used in the manufacture of glass and ceramics as a flux; also crushed for road aggregate and construction material. High-quality specimens with labradorescence (like Moonstone) are used in jewelry.

Geological facts

Feldspars are the most abundant mineral group on Earth, making up about 60% of the crust. This specific specimen shows typical 'twinning' striations on cleavage surfaces that are characteristic of the plagioclase series.

Field identification & locations

Identify in the field by its distinct white-to-pearly color and its rectangular cleavage planes. Look for tiny parallel grooves (striations) on the flat surfaces which distinguish it from Potassium Feldspar. Commonly found in granite, diorite, and gabbro.

Other mineral specimens

See all

Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

Epidote

Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)

metamorphic

Nephrite Jade

Nephrite

Mineral/Rock

Banded Gneiss (River Rock/Pebble)

Gneiss (specifically a banded variety often found as a river rock)

Metamorphic Rock

Green Apatite on Albite

Fluorapatite [Ca5(PO4)3F] on Albite [Na(AlSi3O8)]

mineral

Epidote

Epidote - Ca2(Al2,Fe3+)3(SiO4)3(OH)

mineral