Quartzite

Hardness: 7 (Mohs scale), Color: tan to light orange/yellow due to iron staining, Luster: vitreous to dull, Crystal structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6 - 2.7

Formed through the regional metamorphism of quartz sandstone. Under high heat and pressure, the individual quartz grains recrystallize and fuse together into a dense, interlocking matrix. It is a common component of Precambrian and Paleozoic mountain belts.

Used as crushed stone for road construction, railway ballast, and in the manufacturing of glass and ceramics. Polished varieties are used as decorative stone, countertops, and flooring.

Quartzite is so tough that it often outlasts the mountains it was formed in, remaining as resistant ridges or 'monadnocks' long after softer surrounding rocks have eroded away. It is significantly harder than the sandstone it originates from.

Identify in the field by its extreme hardness (cannot be scratched by steel) and its tendency to break through quartz grains rather than around them, unlike sandstone. It often displays a sugary or crystalline texture on fresh surfaces.