Granite (specifically Rapakivi Granite)

Physical Properties

Hardness: 6-7 Mohs; Color: Pink, orange-red, grey, and black; Luster: Vitreous to dull; Crystal structure: Phaneritic (coarse-grained) with large rounded orthoclase phenocrysts; Specific gravity: 2.63-2.75.

Formation & Geological History

Formed through the slow cooling of silica-rich magma deep within the Earth's crust (plutonic formation). Many Rapakivi granites date to the Proterozoic eon, roughly 1.4 to 1.7 billion years ago.

Uses & Applications

Used extensively in construction for countertops, floor tiles, paving stones, and graveyard monuments. It is also used as crushed stone for road base and high-quality aggregate.

Geological Facts

The term 'Rapakivi' is Finnish for 'crumbly rock,' because the balanced chemical weathering of different minerals often causes these rocks to disintegrate more easily than other granites. It is famous for its 'ovoidal' feldspar crystals.

Field Identification & Locations

Identify in the field by its coarse crystalline texture and the presence of large pinkish potassium feldspar crystals often surrounded by a rim of green-grey plagioclase. Commonly found in the Baltic Shield (Finland/Sweden), parts of North America, and Brazil.

Identified on: 4/25/2026

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