Yellow Quartzite (River Pebble)

Physical Properties

Hardness: 7 on Mohs scale; Color: Yellow, tan, brownish due to iron oxide staining; Luster: Vitreous to waxy (especially when wet); Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & Geological History

Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, causing the sand grains to recrystallize into a dense, interlocking mosaic of quartz crystals. Typically found in ancient mountain belts.

Uses & Applications

Used in construction as crushed stone or ballast, as a decorative stone in landscaping, and sometimes as a minor gemstone or for making stone tools in prehistoric times.

Geological Facts

Quartzite is so tough that it often outlasts the mountain ranges in which it formed, frequently appearing as smooth, rounded pebbles in riverbeds and on beaches long after the surrounding softer rocks have eroded away.

Field Identification & Locations

Identify in the field by its extreme hardness (it will easily scratch glass) and lack of visible individual sand grains (unlike sandstone). Look for smooth, water-worn surfaces and a translucent quality when thin edges are held to light.

Identified on: 4/21/2026

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