Quartzite (Milky Quartz Cobble)

Hardness: 7 (Mohs scale), Color: Creamy white to grayish-white, Luster: Vitreous to greasy, Crystal structure: Trigonal (often microcrystalline in massive form), Cleavage: Indistinct/Conchoidal fracture, Specific gravity: 2.65

Formed from the regional metamorphism of quartz-rich sandstone. Specifically, the sandstone is subjected to intense heat and pressure, causing the individual quartz grains to recrystallize and fuse together. These specimens are often rounded into cobbles by water transport in riverbeds or glacial deposits.

Used primarily in construction as railroad ballast, aggregate in concrete, or for road base. In larger, purer forms, it can be used for manufacturing glass, silicone, or as decorative landscaping stones.

Quartz is one of the most chemically and physically resistant minerals on Earth's surface. Because of its hardness, it often survives long-distance transport in rivers and along coasts, which is why it is one of the most common materials found in river gravel and beach pebbles.

Identify in the field by its inability to be scratched by a steel knife (it will scratch the steel) and its lack of reaction to acid. Look for a sugary or glassy texture on fresh breaks. It is ubiquitous in alluvial deposits and glaciated regions globally.