Granite (Alkali-feldspar Granite)

Physical Properties

Hardness: 6-7 on Mohs scale. Color: Salmon pink/red (due to orthoclase feldspar) with grey quartz and dark biotite or hornblende. Luster: Vitreous to dull. Crystal structure: Phaneritic (coarse-grained). Cleavage: Perfect in two directions for feldspar, none for quartz.

Formation & Geological History

Formed through the slow crystallization of magma below Earth's surface (intrusive). The large crystals indicate it cooled very slowly over thousands of years within the Earth's crust.

Uses & Applications

Used extensively in construction for countertops, monuments, floor tiles, and as crushed stone for road base and concrete aggregate.

Geological Facts

Granite makes up a large portion of the continental crust. The pink or red color in this specific specimen is caused by a high concentration of potassium feldspar (orthoclase), which often contains trace amounts of hematite.

Field Identification & Locations

Identify in the field by its visible interlocking crystals of different colors and its extreme hardness (cannot be scratched by a steel knife). Commonly found in mountainous regions or shield areas like the Canadian Shield or the Appalachians.

Identified on: 4/29/2026

Mode: Standard