Quartzite

Hardness 7 on Mohs scale, grayish-white to tan/rusty brown staining, vitreous to dull luster, granoblastic texture, highly resistant to weathering, non-foliated

Formed from quartz-rich sandstone subjected to high heat and pressure during regional metamorphism, fusing the quartz sand grains together into a dense crystal matrix

Used as decorative landscaping stone, crushed stone aggregate for road construction and ballast, flux in metallurgy, and dimension stone

Quartzite is so tough that it often breaks through the constituent quartz grains rather than along their boundaries, unlike its precursor sandstone which fractures along grain boundaries

Can be identified in the field by its sugary or crystalline texture that cannot be scratched by a steel blade, commonly found in mountain belts, eroded river beds, and glacial till; virtually no value as a individual landscape specimen