Granite / Feldspar Pegmatite
Feldspar-Quartz-Mica Rock / Pegmatite · Mineral Specimen and Geological Rock
Crystal System
Varies by mineral component (Monoclinic, Triclinic, Trigonal, Hexagonal)
Mineral Group
Silicates (Tectosilicates and Phyllosilicates)
Chemical Formula
KAlSi3O8 - NaAlSi3O8 - SiO2 (Complex silicate mixture)
Formation Process
Igneous, formed from the slow cooling and crystallization of magma deep within the Earth's crust, often enriched in volatile elements during the final stages of crystallization.
About This Crystal
A coarse-grained igneous rock fragment displaying an interlocking mosaic of minerals. It shows a granular, crystalline texture with whitish to yellowish-tan feldspar crystals, glassy translucent quartz grains, and possibly tiny flecks of mica, featuring weathered orange-brown iron oxide stains on the exterior surface.
Physical Characteristics
Color ranges from off-white, grey, and tan to pinkish with brownish iron-staining; streak is white; exhibits uneven to sub-conchoidal fracture; specific gravity typically around 2.5 to 2.7; tenacity is hard and brittle.
Optical Properties
Varies by individual mineral constituent. Quartz is uniaxial positive with a vitreous luster; feldspars are biaxial with vitreous to pearly cleavage surfaces.
Hardness & Durability
Origin Region
Worldwide distribution; commonly found in continental shields, mountain-building belts, and major pegmatite fields such as Minas Gerais (Brazil), Madagascar, and various locations in North America.
Hardness & Durability
Mohs hardness typically ranges from 6 to 7 for the bulk aggregate due to the presence of quartz and feldspar. Moderate to good durability for architectural and decorative uses, though sensitive to hydrofluoric acid.
Care & Maintenance
Clean with warm soapy water and a soft brush. Avoid harsh chemical cleaners and abrasive acids. Store away from softer minerals to prevent scratching.
Rarity & Value
Very common. Granite and pegmatitic rocks make up a significant portion of the Earth's continental crust and have low monetary value as raw mineral specimens.
Special Characteristics
Displays a classic coarse-grained phaneritic texture characteristic of intrusive igneous rocks, with clearly distinguishable individual mineral crystals visible to the naked eye.
Lore & History
Historically used extensively in architecture, monuments, and sculpture by ancient civilizations including the Egyptians and Romans. In modern metaphysical traditions, granite is viewed as a stone of strength, grounding, and stability, though these are non-scientific cultural beliefs.