Granite (Alkali Feldspar, Quartz, and Biotite)
Granitic Igneous Rock (composed of orthoclase, quartz, and biotite mica) · Mineral Specimen and Decorative Stone (Plutonic Igneous Rock)
Crystal System
Phaneritic texture (mixed systems); Orthoclase is Monoclinic, Quartz is Trigonal, Biotite is Monoclinic
Mineral Group
Silicates (Tectosilicates and Phyllosilicates)
Chemical Formula
SiO2 (Quartz) + KAlSi3O8 (Orthoclase) + K(Mg,Fe)3AlSi3O10(F,OH)2 (Biotite)
Formation Process
Igneous (Intrusive crystallization); formed by the slow cooling of silica-rich magma deep within the Earth's crust
About This Crystal
A coarse-grained (phaneritic) rock showing interlocking crystals of salmon-pink feldspar, translucent grey quartz, and black flaky biotite. Luster varies from vitreous on quartz to pearly on feldspar cleavages.
Physical Characteristics
Color: Pink, white, grey, and black; Streak: White; Fracture: Uneven; Specific Gravity: 2.63 - 2.75 g/cm3; Some feldspars may show a weak blue fluorescence under UV light
Optical Properties
Visible interlocking grain boundaries; Quartz shows no cleavage and greasy luster; Feldspar shows two cleavage planes at roughly 90 degrees; Biotite shows perfect basal cleavage
Hardness & Durability
Origin Region
Found globally in continental crust; notable sources include Brazil, Norway, India, and the USA (Yosemite, New Hampshire)
Hardness & Durability
Mohs hardness 6 to 7; very high durability and toughness; resistant to most household acids and weathering
Care & Maintenance
Wash with warm soapy water; generally safe for ultrasonic cleaners. Avoid harsh hydrofluoric acid. Granite is porous and can stain if not sealed in commercial applications
Rarity & Value
Common; value is determined by aesthetic color patterns and crystal size for large slabs; mineral specimens are abundant and inexpensive
Special Characteristics
Phaneritic texture (visible crystals); presence of biotite mica flakes creates a 'sparkle' or metallic glitter effect under direct light
Lore & History
Historically used in ancient Egyptian obelisks and pyramids; symbolizes endurance and grounding. In modern lore, it is believed to help with 'the big picture' and stability.