Quartzite

Hardness: 7 (Mohs scale), Color: tan to creamy white, Luster: dull to vitreous, Structure: granular and non-foliated, Cleavage: none (conchoidal fracture), Specific Gravity: 2.6-2.7

Formed from the metamorphism of quartz sandstone under intense heat and pressure, typically during tectonic plate collisions and mountain-building events. The original sand grains recrystallize into a locked interlocking mosaic of quartz.

Used as building stone, decorative landscaping rock, railway ballast, and in the production of glass and silicon due to high silica content.

Quartzite is so tough that it often outlasts the surrounding rocks in a landscape, forming prominent ridges and peaks. It is often confused with marble, but can be distinguished by its hardness; quartzite will scratch glass while marble will not.

Identify by its extreme hardness and granular texture that looks like sandpaper but is smooth to the touch. Found globally in ancient mountain belts and riverbeds as rounded pebbles.