Granite
Plutonic Igneous Rock (Granite) · Decorative Stone / Industrial Mineral / Common Rock Specimen
Crystal System
Polycrystalline/Phaneritic; individual minerals present as Trigonal (Quartz), Monoclinic/Triclinic (Feldspar), and Monoclinic (Mica).
Mineral Group
Silicates (primarily Tectosilicates and Phyllosilicates)
Chemical Formula
KAlSi3O8 – NaAlSi3O8 – CaAl2Si2O8 (Feldspar) + SiO2 (Quartz) + K(Mg,Fe)3AlSi3O10(OH)2 (Biotite)
Formation Process
Igneous (Intrusive/Plutonic). It forms from the slow cooling and crystallization of magma deep beneath the Earth's surface at high pressure.
About This Crystal
A coarse-grained phaneritic rock showing a salt-and-pepper appearance. It features interlocking crystals of translucent gray quartz, white to pinkish opaque feldspar, and dark speckles of mafic minerals like biotite mica or hornblende. The texture is rough and crystalline.
Physical Characteristics
Color: Grayish-white with pink and black spots; Streak: White; Cleavage: None for the rock itself, though feldspars within show perfect cleavage; Fracture: Uneven; Specific Gravity: 2.63 - 2.75 g/cm³; Luster: Vitreous to dull.
Optical Properties
Generally opaque as a bulk rock; individual quartz crystals exhibit low birefringence and are singly refractive; feldspars may show twinning under magnification.
Hardness & Durability
Origin Region
Found worldwide in continental crust; notably from India, Brazil, China, and the USA. Forms in the deep roots of mountain ranges.
Hardness & Durability
Mohs hardness of approximately 6 to 7 (based on quartz and feldspar content). Highly durable, resistant to weathering, and possesses high compressive strength.
Care & Maintenance
Hardy and stable. Can be cleaned with warm soapy water and a soft brush. Resistant to most household chemicals but can be stained by oils if left unsealed.
Rarity & Value
Very Common. Value is generally low for small specimens; price increases significantly for large, high-quality slabs used in architecture or monuments.
Special Characteristics
Phaneritic texture (visible crystals); individual mica flakes may exhibit a 'glitter' effect (schiller) when reflecting light; highly resistant to acid rain compared to carbonate rocks.
Lore & History
Historically used by the Ancient Egyptians for pyramids and obelisks due to its strength. It symbolizes endurance and groundedness. In modern culture, it is the standard for longevity in memorials and structural foundations.