Quartzite

Hardness: 7 (Mohs scale), Color: tan, grey, brown, or pinkish based on iron content and impurities, Luster: vitreous to dull, Crystal structure: granular/non-foliated, Cleavage: none (fractures through grains), Specific Gravity: 2.6-2.7

Formed through the metamorphism of quartz-rich sandstone. High heat and pressure cause the original quartz grains to recrystallize and fuse together. These are often found in riverbeds as water-smoothed cobbles or in mountainous regions where tectonic activity occurred.

Commonly used in construction for road ballast, railroad ballast, and building stone. Highly polished specimens are used as decorative flooring, countertops, or in landscaping. Collectors value naturally tumbled river stones for their smooth texture and durability.

Quartzite is one of the most durable rocks on the Earth's surface. Unlike sandstone, which breaks around the individual sand grains, quartzite is so strongly fused that it breaks right through the grains when fractured.

Identify in the field by its extreme hardness (it will easily scratch glass or steel) and its granular appearance. These river-worn specimens are ubiquitous in fluvial environments, especially in areas with ancient metamorphic bedrock. Collectors look for unique banding or internal patterns.