Red Quartzite Cobble

Physical Properties

Hardness: 7 (Mohs scale), Color: Reddish-pink to light brown, Luster: Vitreous to dull, Crystal Structure: Trigonal/Hexagonal (microcrystalline), Cleavage: None, Specific Gravity: 2.6-2.7

Formation & Geological History

Formed from quartz-rich sandstone subjected to extreme heat and pressure during regional metamorphism. The red color is typically due to iron oxide impurities (hematite). Many specimens in this rounded form are fluvial or glacial cobbles.

Uses & Applications

Used as decorative garden stone, in construction aggregates, as railroad ballast, and sometimes in lapidary work for making polished 'river stones'.

Geological Facts

Quartzite is so tough that it often survives intense weathering that destroys other rocks. It is harder than steel and will easily scratch glass.

Field Identification & Locations

Identify in the field by its hardness and 'sugary' texture on a fresh break. Commonly found in riverbeds, glacial tills, or areas with exposed Proterozoic shield rock. Unlike sandstone, when quartzite breaks, it fractures through the quartz grains rather than around them.

Identified on: 4/23/2026

Mode: Standard