Blue Quartzite

Hardness: 7 Mohs scale; Color: Blue-grey to muffled blue; Luster: Vitreous to dull; Crystal structure: Trigonal (granular); Cleavage: None; Specific gravity: 2.6-2.7

Formed via the metamorphism of quartz sandstone. High pressure and heat cause the sand grains to recrystallize into a dense network of interlocking quartz crystals. The blue hue often results from Rayleigh scattering of light by microscopic inclusions or presence of minerals like dumortierite.

Used in construction for flooring and road ballast, as dimension stone in architecture, and in lapidary for carvings, beads, and jewelry.

Unlike sandstone, quartzite is extremely durable and will break through the grains rather than around them. It is one of the hardest and most chemically resistant rocks found on the Earth's surface.

Identify in the field by its grainy, sugary texture and extreme hardness (it will easily scratch glass). Look for it in mountainous regions or ancient metamorphic belts.