Quartzite

Hardness 7 on Mohs scale; color is off-white to yellowish-tan due to iron staining; luster is vitreous to dull; granular texture with no visible cleavage; very durable.

Formed through the metamorphism of quartz-rich sandstone. High heat and pressure causes quartz grains to recrystallize and fuse together, creating an extremely hard and dense rock mass.

Used in construction as crushed stone for road grit and railroad ballast, in glass manufacturing, and as decorative stone in landscaping. Its durability makes it resistant to weathering.

Quartzite is so hard that it will scratch glass. It is often confused with marble, but unlike marble, quartzite will not fizz when exposed to acid. Many of the oldest mountain ranges are composed of quartzite due to its extreme resistance to erosion.

Identify in the field by its hardness (scratches steel) and its granular, sugary appearance on fresh surfaces. It is found in mountain belts worldwide, particularly in areas with ancient sedimentary sequences.