Quartzite
Image: James St. John (CC BY 2.0)
Mineral NameQuartzite
Chemical FormulaSiO2
Mohs Hardness7
Crystal Systemtrigonal
Lustervitreous
Streak Colorwhite
Cleavagenone
Fractureconchoidal
Specific Gravity2.65
Colorsreddish-purple, pink, white, gray, yellow, brown, green, blue, black
Transparencytranslucent
Type LocalitySioux Falls, Transcontinental Arch, South Dakota, USA
Mineral GroupMetamorphic Rock (composed primarily of quartz, a silicate mineral)
Usesbuilding material, road aggregate, decorative stone, abrasives
Associated Mineralsquartz, feldspar, mica, hematite, magnetite
Raritycommon
Description
This sample is a reddish-purple, fine-grained metamorphic rock with a sugary texture, showing interlocking quartz crystals and some lighter streaks. It is hard and does not react with acid.
Geological Context
Quartzite is an intermediate- to high-grade metamorphic rock formed by the metamorphism of quartzose sandstones or siltstones. This specific sample is from the Paleoproterozoic Sioux Quartzite, dating back 1.65 to 1.70 billion years.
