igneous
Feldspar Rich Granite with Limonite Staining
K-Feldspar Granite (KAlSi3O8)
Hardness: 6.0-6.5 (Mohs scale), Color: Creamy white to pale gray with yellowish-orange iron staining, Luster: Vitreous to pearly, Crystal structure: Monoclinic or triclinic, Cleavage: Two directions at nearly 90 degrees.
- Hardness
- 6
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Physical properties
Hardness: 6.0-6.5 (Mohs scale), Color: Creamy white to pale gray with yellowish-orange iron staining, Luster: Vitreous to pearly, Crystal structure: Monoclinic or triclinic, Cleavage: Two directions at nearly 90 degrees.
Formation & geological history
Formed through the slow cooling of silica-rich magma deep within the Earth's crust (plutonic). The specimen shows signs of chemical weathering where iron-bearing minerals have oxidized into limonite.
Uses & applications
Used extensively as dimensional stone in construction, countertops, and floor tiles. Finely ground feldspar is vital in the ceramics and glass manufacturing industries as a flux.
Geological facts
Granite makes up a significant portion of the Earth's continental crust. The yellow-orange 'rust' seen on this specimen is likely limonite, an iron oxide that forms when groundwater reacts with iron-rich minerals like biotite or pyrite.
Field identification & locations
Identify in the field by its interlocking crystalline texture and hard surface that cannot be scratched by a steel knife. Commonly found in mountainous regions or shield areas like the Appalachians or the Canadian Shield.
