Idaho State Stone
Like all quartzite, Idaho quartzite is a hard, medium-grained metamorphic rock. The high mica content of Idaho quartzite gives it a characteristic sheen and a tendency to form in easily separable layers less than an inch thick. Its color comes in an attractive earthy palette of yellows, browns, silver-grays, and off-whites.
REPRESENTATIVE OF IDAHO
While Idaho has not designated an official state stone, Idaho quartzite, also known as Rocky mountain quartzite or Oakley stone, has earned a name for itself as a distinctive, useful and attractive stone. A relative latecomer to the U.S. stone market, it has been quarried in the City of Rocks area of Idaho since the 1940s and is now marketed both across the U.S. and in Canada and Europe, lending some of Idaho’s rugged beauty to locations where it is installed.
Quartzite forms from metamorphism of sandstone. As its name suggests, quartzite is the stone relative of the mineral quartz; the chemical composition of quartzite, quartz, and sandstone is identical. The difference lies in how they form. Quartz is a mineral, growing in crystals. Sandstone is a sedimentary rock formed from sand (which is mostly tiny bits of quartz). When sandstone is subjected to high heat and pressure inside the earth, it forms quartzite, a stone with hardness and weather-resistance comparable to granite. Thus, most quartzite is favored as a building stone.
Much of the Idaho quartzite, on the other hand, metamorphosed from sedimentary layers of sandstone interspersed with layers high in clay content. The high temperature and pressure that caused the quartz-rich sandstone to metamorphose into quartzite also transformed the clay layers into mica. The foliated structure of the stone, while not suitable for cutting massive blocks, gives it superior coverage as a veneer and paving material.
In 2006, four Idaho quarries produced 466,000 metric tons of crushed quartzite worth over $2 million. One quarry produced quartzite for dimension stone.
Being a metamorphic rock, quartzite occurs in areas that have been subjected to high temperature and pressure in geologic history. Not surprisingly, it is associated with mountains that have grown up at the convergence of tectonic plates.
Quartzite is found in many U.S. states from coast to coast, notably in Wisconsin, Idaho, Utah, and Arizona. North of the border in Ontario, Canada, quartzite makes up the Cloche Range of mountains. Significant surface formations of quartzite appear in the United Kingdom. The largest quartzite deposits are in Norway.
Apart from its use as a structural stone, typical quartzite is used as a decorative architectural element on walls, roofs, floors, and stairs. Idaho quartzite, as mentioned, is usually used in decorative architectural applications such as paving and stone cladding. Crushed quartzite is sometimes used in road construction. Industrial products made from quartzite are ferrosilicon (for steel production), industrial sand, silicon metal, and carborundum.
Chemical Formula: SiO2
Color: Occurs in an infinite range of colors. Most commonly white, purple, brown, and colorless
|Author: World Trade Press|