Quartzite is a metamorphic rock, while quartz is an igneous rock that crystallizes from magma or precipitates around hydrothermal vents. Sandstone under pressure becomes quartz arenite and quartzite, but quartzite does not become quartz. The construction industry further complicates the matter. If you buy “quartz” for countertops, it is actually an engineered material made from crushed quartz, resin, and pigments and not natural rock. Another rock commonly confused with quartzite is a marble. Both quartzite and marble are usually pale, leafless rocks. Similar in appearance, marble is a metamorphic rock composed of recrystallized carbonate minerals rather than silicate. Marble is softer than quartzite. A good test to distinguish between the two is to apply vinegar or lemon juice to the stone. Quartzite is not affected by weak acid etching, but marble.
Quartzite’s strength and toughness are useful in many applications. Crushed quartzite is used for road construction and railroad ballast. Used in the manufacture of roof tiles, stairs and floors. When you cut and polish the stone, it is very beautiful and durable. It is used to make kitchen countertops and decorative walls.
Quartzite geology and uses
-Quartzite is a leafless metamorphic rock mainly composed of quartz. It is usually white to light gray rock, but occurs in other colors such as red and pink (from iron oxide), yellow, blue, green, and orange. The stone has a grainy surface with the texture of sandpaper, but can be polished to a glassy luster. Quartzite is formed when pure or near-pure quartz sandstone is exposed to heat and pressure. This is usually caused by tectonic movements. The sandstone grains melt and recrystallize and bond with silica. Quartzite arenite is the intermediate stage between sandstone and quartzite. Arenite is still considered to be sedimentary rock, but it has an extremely high quartz content. However, the transition from sandstone to quartzite is difficult to see. Some geologists use the term “quartzite” to refer to metamorphic rocks that are almost entirely composed of quartz.Here, quartzite is identified as cracks across grain boundaries, while quartzite cracks around them. Other geologists simply identify “quartzite” as the densely cemented rock found above or below the sedimentary quartzite belt.
Quartzite is almost entirely composed of silicon dioxide, SiO2. With a purity of about 99% SiO2, this rock is called local quartzite. Otherwise, quartzite usually contains iron oxide and may contain trace minerals rutile, zircon and magnetite. Quartzite may contain fossils.
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Quartzite Rock Geology and Uses by By Anne Marie Helmenstine, Ph.D.