Quartzite

Hardness: 7 (Mohs scale), Color: Grayish-purple to brown, Luster: Vitreous to dull, Crystal structure: Granular, Cleavage: None (conchoidal fracture), Specific gravity: 2.6-2.7

Formed through the regional metamorphism of quartz-rich sandstone under intense heat and pressure, causing recrystallization of quartz grains into a dense interlocking network. This specimen likely dates from the Proterozoic to Paleozoic eras.

Used primarily as crushed stone for road construction, railway ballast, and as a decorative building stone or countertop material due to its extreme durability and resistance to weathering.

Quartzite is so hard and chemically stable that quartzite ridges often form prominent topographic highs because they resist erosion much better than surrounding rocks. It was historically used to make stone tools by prehistoric humans.

Identify it by its ability to scratch glass and lack of reaction to acid. In the field, look for a sugary or crystalline texture where individual sand grains are no longer visible. Common in mountain belts like the Appalachians or the Alps.