mineral

Plagioclase Feldspar (specifically Albite/Oligoclase)

(Na,Ca)(Si,Al)4O8

Hardness: 6.0-6.5 on Mohs scale; Color: white, grayish, or colorless; Luster: Vitreous to pearly; Crystal structure: Triclinic; Cleavage: Two perfect cleavages at nearly 90 degrees; Specific gravity: 2.62-2.76. Key visual feature: Polysynthetic twinning striations (fine parallel lines) on cleavage faces.

Hardness: 6
Color: white, grayish, or colorless
Luster: Vitreous to pearly

Identified March 11, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the crystallization of igneous magma or during the metamorphism of other rocks. It is one of the most common minerals in the Earth's crust, occurring in nearly all igneous rocks and many metamorphic ones throughout various geological ages.

Uses & applications

Used extensively in the glass and ceramics industries as a flux. It is also used in the manufacture of enamels, scouring soaps, and as a filler in paints and plastics. Certain iridescent varieties like Sunstone or Moonstone are used in jewelry.

Geological facts

Feldspars make up about 60% of the Earth's crust. The specific parallel lines seen in the image are called 'twinning striations,' which are a diagnostic feature used to distinguish plagioclase from orthoclase feldspar.

Field identification & locations

Identify in the field by looking for the 'record-player' grooves (striations) on flat, shiny cleavage surfaces under a hand lens. Commonly found in granites, basalts, and diorites globally. Collectors should look for large, well-formed crystals in pegmatites.

Other mineral specimens

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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