Quartzite (likely Iron-stained)

Hardness: 7 (Mohs), Color: Tan to yellow-brown (due to iron oxide staining), Luster: Vitreous to dull, Crystal Structure: Trigonal (microcrystalline), Cleavage: None, Specific Gravity: 2.63-2.65

Quartzite forms through the metamorphism of quartz-rich sandstone. High heat and pressure in regional metamorphic zones cause the quartz grains to recrystallize and fuse together, creating a very durable rock. This specific sample shows surface weathering and iron staining from groundwater exposure.

Used extensively in road construction, railroad ballast, and as a decorative stone. High-purity quartzite is used to produce glass, silicon metal, and abrasives. In jewelry, it is sometimes tumbled as a common stone.

Quartzite is so tough that it often survives intense mechanical weathering, causing it to remain as ridges on mountain ranges. It is harder than steel and will easily scratch glass.

Identify by its extreme hardness (cannot be scratched by a knife) and its grainy, 'sugary' texture. Unlike sandstone, quartzite breaks through the quartz grains rather than around them. Found globally in ancient mountain belts and river beds.