Granodiorite
Phaneritic Igneous Rock (Granodiorite) · Decorative Stone / Industrial Mineral / Common Rock
Crystal System
Polycrystalline/Massive. Individual minerals include Triclinic (Plagioclase), Monoclinic (Biotite/Orthoclase), and Trigonal (Quartz).
Mineral Group
Silicates (specifically Tectosilicates and Phyllosilicates within an igneous rock matrix)
Chemical Formula
Complex mixture: (Na,Ca)(Si,Al)4O8 (Plagioclase), KAlSi3O8 (Orthoclase), SiO2 (Quartz), K(Mg,Fe)3(AlSi3O10)(OH,F)2 (Biotite)
Formation Process
Igneous: Forms from the slow cooling and crystallization of silica-rich magma deep underground (plutonic), allowing large visible crystals to grow.
About This Crystal
A medium-to-coarse grained phaneritic rock. It displays a 'salt and pepper' appearance with white to light grey plagioclase, glassy grey quartz, and black specks of biotite mica or hornblende. The specimen in the image is well-rounded, likely due to river or glacial erosion, with an earthy to sub-vitreous luster.
Physical Characteristics
Color: Mottled white, grey, and black. Streak: White (on individual minerals). Cleavage: Distinct in feldspars, none in quartz, basal in mica. Specific Gravity: 2.65 - 2.73. Non-magnetic. Non-fluorescent.
Optical Properties
Generally opaque as a hand specimen. Individual quartz grains show low birefringence; plagioclase may show polysynthetic twinning under polarized light.
Hardness & Durability
Origin Region
Worldwide; notably the Sierra Nevada batholith (USA), and various shields in Brazil, Canada, and Australia. Forms in continental arc magmatism.
Hardness & Durability
Mohs hardness 6 to 7 (average of component minerals). Highly durable, weather-resistant, and excellent for structural use.
Care & Maintenance
Extremely low maintenance. Clean with warm soapy water. Resistant to most household chemicals, though acidic cleaners can dull the surface over long periods.
Rarity & Value
Very Common. Low monetary value as a specimen, but high commercial value as 'granite' for countertops, flooring, and monuments.
Special Characteristics
Phaneritic texture (visible crystals), interlocking crystalline structure, and occasional pinkish orthoclase staining (visible at the bottom right of the specimen).
Lore & History
Historically used in ancient Egyptian architecture (e.g., the Rosetta Stone is carved on granodiorite). Metaphysically, it is traditionally associated with grounding, stability, and endurance due to its geological permanence.