Ferruginous Quartz Cobble

Physical Properties

Hardness: 7 (Mohs scale); Color: Tan, brown, orange, and white (stained by limonite/hematite); Luster: Vitreous to greasy; Crystal structure: Trigonal/Hexagonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Formation & Geological History

Formed from silica-rich hydrothermal fluids or within igneous/metamorphic environments. This specific specimen is a 'river rock' or cobble, shaped by alluvial erosion (water transport) over thousands of years.

Uses & Applications

Used primarily in landscaping, construction aggregate, and as a material for flint-knapping or lapidary tumbling. High-purity quartz is used in glass and electronics.

Geological Facts

Quartz is the second most abundant mineral in Earth's continental crust. The yellow-brown staining on this specimen is caused by iron oxide 'rusting' into the microscopic fissures of the stone.

Field Identification & Locations

Identify by its ability to scratch glass, its lack of cleavage, and its rounded, water-worn exterior. Found globally in river beds, beaches, and glacial till.

Identified on: 4/21/2026

Mode: Standard