Quartzite

Hardness: 7 (Mohs scale), Color: Pinkish-red to purple (due to iron oxides), Luster: Vitreous to dull, Crystal Structure: Granular/Massive, Texture: Sugary or interlocking crystals

Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse into a dense, hard rock. This specimen appears to be water-worn in a fluvial environment.

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

Quartzite is so tough that it often survives intense glacial and fluvial transport where softer minerals disintegrate. Unlike sandstone, when quartzite breaks, the fracture goes through the quartz grains rather than around them.

Identify in the field by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. Often found in riverbeds or glacial deposits as rounded cobbles. This specific color is common in the Baraboo Quartzite of Wisconsin or similar Precambrian formations.