Quarzit

Quarzit, or quartzite in English, is a hard, non-foliated metamorphic rock composed almost entirely of quartz. It forms when quartz-rich sandstone undergoes metamorphism, typically through exposure to elevated temperatures and pressures during regional or contact metamorphism. The original sandstone grains recrystallize and fuse into an interlocking mosaic of quartz crystals, often with a distinct glassy to pearly luster.

In hand specimen, quartzite is usually massive and very dense, with a granular texture that resists weathering. It has a Mohs hardness of about 7, exhibits conchoidal fracture, and displays high compressive strength. The color ranges from light gray or white to pink, red, or yellow, depending on impurities such as iron oxides or other minerals.

Quartzite is used primarily as a dimension stone and decorative building material. It is cut into slabs for countertops, tiles, and paving, or crushed for use as an aggregate in construction. Its hardness and aesthetic variability make it a popular choice for facades, flooring, and garden features. It is important to distinguish quartzite from quartz sandstone, which is softer and not fully recrystallized.

Geographically, quartzite occurs in many metamorphic belts worldwide, often associated with ancient quartz-rich sandstones that were buried and recrystallized during mountain-building events.

The Terminology: Quarzit is the German term; quartzite is the corresponding English term.