Quartzite

Hardness: 7 (Mohs), Color: Light tan, white, or grey, Luster: Vitreous to dull, Crystal Structure: Trigonal (granular texture), Specific Gravity: 2.6-2.7

Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure reciprocal to tectonic plate activity cause quartz grains to recrystallize and fuse.

Used in construction as crushed stone for road beds, as dimension stone for wall coverings and flooring, and in the manufacturing of glass and ceramics due to high silica content.

Quartzite is so tough that it often breaks through the individual quartz grains rather than around them, unlike sandstone. It is extremely resistant to chemical weathering.

Identify in the field by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. Often found in mountain ranges or shield areas where ancient seabeds were buried and compressed.