Quartzite River Rock (with Limonite staining)

Physical Properties

Hardness: 7 on Mohs scale; Color: Tan, orange-brown (due to iron oxide coating), white internally; Luster: Dull/waxy exterior, vitreous interface; Structure: Granular, non-foliated; Cleavage: None (conchoidal fracture); SG: 2.6-2.7.

Formation & Geological History

Originally formed as sandstone (sedimentary) and later subjected to intense heat and pressure (metamorphism) which fused quartz grains together. This specific specimen shows rounding from water erosion in a high-energy environment like a riverbed.

Uses & Applications

Used as crushed stone for road construction, railway ballast, and decorative landscaping. High-purity quartzite is also used to produce silica sand for glassmaking.

Geological Facts

Quartzite is so tough that it often outlasts the surrounding rock in weathering processes, resulting in the rounded 'cobbles' often found in glacial till and stream beds. The orange color on this piece is 'desert varnish' or limonite staining from iron minerals.

Field Identification & Locations

Identify by its ability to easily scratch glass and its lack of reaction to acid. Look for a sugary texture on broken surfaces. Very common in riverbeds across North America and Europe.

Identified on: 4/14/2026

Mode: Standard