Quartzite

Hardness: 7 (Mohs scale), Color: Pinkish-red (from iron oxide impurities), Luster: Vitreous to dull, Crystal Structure: Trigonal (granular), Cleavage: None, Specific Gravity: 2.6-2.7

Formed through the regional metamorphism of quartz sandstone. Intense heat and pressure cause the quartz grains to recrystallize and fuse together. These rocks are found in ancient mountain belts and shield areas around the globe.

Used as decorative stone in landscaping, dimension stone for flooring and walls, railway ballast, and occasionally as a source of silica for glass manufacturing.

Quartzite is so hard that it will scratch glass and even high-grade steel. It is often more resistant to weathering than the surrounding rock, leading it to form prominent ridges and hills.

Identify in the field by its sugary, granular texture and its inability to be scratched by a knife. Unlike sandstone, quartzite fractures through the grains rather than around them. Found commonly in the Appalachian Mountains and the Lake Superior region.