Quartzite Cobble

Hardness: 7 (Mohs scale), Color: light grey to white with tan staining, Luster: Vitreous to dull, Crystal Structure: Granular/Crystalline, Specific Gravity: 2.6-2.7. Very durable and non-fissile.

Formed from the regional metamorphism of quartz-rich sandstone. High heat and pressure caused sand grains to recrystallize and fuse together. These specific specimens are water-worn and likely found in a riverbed or glacial deposit.

Used in construction as crushed stone for road ballast, as a decorative garden rock, and in the manufacturing of glass and ceramics when high purity quartz is present.

Quartzite is so tough that it often outlasts the mountain ranges it was formed in, becoming the primary component of river gravel and glacial till. Unlike sandstone, quartzite fractures across the sand grains rather than around them.

Identify by its extreme hardness (cannot be scratched by steel) and lack of visible individual sand grains compared to sandstone. It often has a slightly sugary or crystalline appearance on fresh surfaces.