mineral
Feldspar (Orthoclase/Potassium Feldspar)
KAlSi3O8 (Potassium Aluminum Silicate)
Hardness: 6 (Mohs); Color: Pinkish-orange, peach, to tan; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Two directions at 90 degrees; Specific Gravity: 2.55-2.63
- Hardness
- 6 (Mohs)
- Color
- Pinkish-orange, peach, to tan
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 6 (Mohs); Color: Pinkish-orange, peach, to tan; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Two directions at 90 degrees; Specific Gravity: 2.55-2.63
Formation & geological history
Formed primarily in intrusive and extrusive igneous rocks (like granite and rhyolite) through the cooling of magma. Also forms in metamorphic rocks such as gneiss. It is a major component of the Earth's crust.
Uses & applications
Used in the manufacture of glass, ceramics (glazes and porcelain), and as a filler in paints and plastics. Finer specimens are used in jewelry as moonstone or sunstone.
Geological facts
Feldspar accounts for approximately 60% of the Earth's crust. The name is derived from the German 'Feldspath', meaning 'field spar' because of its common appearance in rural fields.
Field identification & locations
Identify in the field by its distinct salmon-pink color, blocky rectangular cleavage, and hardness (will scratch glass but be scratched by quartz). Commonly found in granite outcrops and gravel beds worldwide.
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sedimentary
Schist
Schist
Metamorphic
Epidote
Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)
metamorphic
Gypsum (variety Selenite or Alabaster)
Calcium sulfate dihydrate (CaSO4·2H2O)
Mineral
Nephrite Jade
Nephrite
Mineral/Rock
Banded Gneiss (River Rock/Pebble)
Gneiss (specifically a banded variety often found as a river rock)
Metamorphic Rock