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The second most abundant mineral in the Earth’s continental crust (after the feldspars ), made up of silicon and oxygen (SiO2). It makes up more than 10% of the crust by mass.
There are a wide variety of types of quartz: onyx, agate, and petrified wood are fibrous, microcrystalline varieties collectively known as chalcedony. Although agate is naturally banded with layers of different colors and porosity, commercial varieties of agate are often artificially colored.
Flint, chert, and jasper are granular microcrystalline varieties of quartz, with the bright red color of jasper due to the inclusion of small amounts of iron within the mineral structure.
The most common, coarsely crystalline varieties include massive quartz veins, the distinct, well formed, crystals of “rock crystal”, and an array of colored quartz, including amethyst (purple), rose quartz (pink), smoky quartz (gray), citrine (orange), and milky quartz (white).


A hard metamorphic rock that was originally sandstone. Quartzite usually forms from sandstone that was metamorphosed through tectonic compression within orogenic belts.
Quartzite is quarried for use as a building and decorative stone.


A geologic time period that extends from 2.6 million years ago to the present. This period is largely defined by the periodic advance and retreat of continental glaciers.
The Quaternary is part of the Cenozoic.