mineral

Feldspar (specifically Orthoclase or Plagioclase)

Potassium Aluminum Silicate (KAlSi3O8) or Sodium/Calcium Aluminum Silicate

Hardness: 6 on Mohs scale; Color: White to tan with orange iron staining; Luster: Vitreous to pearly; Crystal structure: Monoclinic or Triclinic; Cleavage: Two planes at nearly 90 degrees; Specific gravity: 2.55-2.76

Hardness: 6 on Mohs scale
Color: White to tan with orange iron staining
Luster: Vitreous to pearly

Identified May 25, 2026More mineral →

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Physical properties

Formation & geological history

Formed during the crystallization of intrusive and extrusive igneous rocks, as well as in many metamorphic and sedimentary rocks. This specimen likely originated from a pegmatite or granite formation.

Uses & applications

Used in the manufacture of glass and ceramics, as a filler in paint and rubber, and occasionally as a gemstone (such as moonstone or sunstone) if high quality.

Geological facts

Feldspar is the most abundant group of minerals in the Earth's crust, making up about 60% of terrestrial rocks. The orange staining in this specimen is likely due to iron oxide (limonite) infiltration into the cleavage planes.

Field identification & locations

Identify in the field by its distinct 90-degree cleavage planes, 'stair-step' appearance when broken, and inability to be scratched by a steel pocket knife but can be scratched by quartz.

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

Biotite Schist

Biotite-rich Schist [K(Mg,Fe)3AlSi3O10(F,OH)2]

metamorphic

Green Apatite on Albite

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

mineral