Quartzite

Hardness: 7 (Mohs scale), Color: tan, buff, or white but can vary, Luster: vitreous to grainy, Crystal Structure: trigonal (microcrystalline), Cleavage: none, Specific Gravity: 2.6 - 2.8

Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together, forming a dense, interlocking matrix.

Primarily used in construction for road ballast, flooring, and wall coverings. Due to its hardness, it is also used for abrasives and as a source of silica in glass manufacturing.

Quartzite is so tough that it often survives erosion better than the surrounding rocks, creating prominent ridges or hills. It can be distinguished from sandstone because it breaks through the grains, not around them.

Identify by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. Often found in mountainous regions or ancient riverbeds as smooth river cobbles. Look for grainy textures that sparkle slightly under light.