Limonite-stained Granite

Physical Properties

Hardness: 6-7 (Mohs); Color: Pinkish-red base with yellow-orange limonite staining; Luster: Dull to vitreous; Structure: Phaneritic (medium-grained crystals) including quartz, orthoclase feldspar, and biotite mica; Specific Gravity: 2.63-2.75

Formation & Geological History

Formed through slow crystallization of magma below Earth's surface. The orange-yellow surface is a secondary weathering effect where iron-bearing minerals (like biotite or pyrite) oxidize into limonite in the presence of water and oxygen.

Uses & Applications

Granite is used extensively in construction, countertops, and decorative gravel. Iron-oxide stained versions are often used in landscaping or for geological study of weathering processes.

Geological Facts

Limonite was once used as a primary yellow pigment for paints and is one of the oldest known pigments used by humans for cave drawings. The pink/red color of the rock itself suggests high potassium feldspar content.

Field Identification & Locations

Identify by its crystalline texture and the way the yellow-orange coating can often be scratched or found localized to joints and surfaces. Commonly found in batholiths and continental crustal shields.

Identified on: 5/13/2026

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