Metaquartzite

Metaquartzite is the metamorphic variety of quartzite, formed when a quartz-rich sandstone is recrystallized by heat and pressure until the original grains and the cement between them fuse into an interlocking mosaic of quartz. The term "metaquartzite" emphasizes the metamorphic origin, distinguishing it from "orthoquartzite," a sedimentary sandstone cemented by silica without metamorphism.

The rock is extremely hard and tough, breaking through the grains rather than around them, which gives it a smooth, sometimes glassy fracture. It is usually white or grey but can be pink, red, or other colors from minor impurities.

Metaquartzite is durable and chemically resistant, making it a long-lasting rock in landscapes and construction.

Metaquartzite forms by regional or contact metamorphism of quartz sandstone (or chert). Rising temperature and pressure cause the quartz grains to recrystallize and the silica cement to merge with them, eliminating the original pore space and grain boundaries to produce a solid, fused quartz fabric.

Because quartz is already stable over a wide range of conditions, metaquartzite can form at relatively low grade through to high grade, with the texture becoming more thoroughly interlocked at higher grade. Impurities like iron oxide, mica, or feldspar add color and minor accessory minerals.

Metaquartzite occurs widely in mountain belts and shields, often forming resistant ridges.

Identify metaquartzite by its great hardness (scratches glass and steel, Mohs 7) and the way it fractures through the grains, producing a smooth to glassy, sugary surface rather than the granular break of sandstone. Unlike sandstone, it does not crumble and grains are not individually loosened.

Luster is glassy to greasy on fresh fracture; streak is white. Distinguish it from sedimentary (ortho)quartzite, which breaks around grains and may feel granular, and from marble, which is much softer (Mohs 3) and fizzes in acid. Metaquartzite does not react with acid and lacks the foliation of schist (unless mica-bearing).

Metaquartzite is valued for its hardness and durability. It is widely used as crushed stone and aggregate for roads, railway ballast, and concrete, and as dimension and decorative stone for countertops, flooring, and facing where its toughness is an asset.

Its high silica purity makes some metaquartzite a source of silica for glassmaking, ceramics, and the production of ferrosilicon and silicon. Colorful varieties are cut as ornamental slabs.

It has minimal metaphysical tradition of its own. Geologically, resistant metaquartzite ridges are important landscape and stratigraphic markers.