Quartzite

Hardness: 7 (Mohs scale), Color: tan, grey, white with rusty iron staining, Luster: vitreous to dull, Crystal structure: Trigonal (granular texture), Specific Gravity: 2.6-2.7

Formed from the regional or contact metamorphism of quartz-rich sandstone under intense heat and pressure, often during mountain-building events.

Used as crushed stone for road construction, railway ballast, and as a decorative stone in landscaping or heavy-duty countertops.

Quartzite is so hard and chemically resistant that it often forms the resistive ridges and peaks of mountain ranges, as it outlasts surrounding softer rocks during erosion.

Identify by its ability to scratch glass and its granular, sugary appearance. Unlike sandstone, it will break through the individual quartz grains rather than around them. Found in ancient mountain belts.