Quartzite

Hardness: 7 (Mohs scale), Color: tan to milky white with brown iron staining, Luster: Vitreous to waxy (on polished surfaces), Structure: Non-foliated granoblastic.

Formed through the regional metamorphism of quartz-rich sandstone under intense heat and pressure. The individual quartz grains recrystallize and fuse into a solid, interlocking network.

Used widely in construction as crushed stone, road ballast, or ornamental cladding. Polished specimens are used in landscaping, as worry stones, or decorative aquarium gravel.

Quartzite is so durable that it often remains as the tops of ridges and mountains because it resists weathering far better than the surrounding rock types.

Identify in the field by its extreme hardness (it will easily scratch glass) and lack of reaction to acid. It often appears as rounded river pebbles or smooth glacial clasts due to its durability. Found worldwide in ancient mountain belts.