Quartz is a hard white or colorless mineral consisting of silicon dioxide, found widely in igneous, metamorphic, and sedimentary rocks. It is the second most abundant mineral in the Earth's continental crust, after feldspar. Quartz is hard and can easily scratch glass.

Quartz is also the most varied of all minerals, occurring in all different forms and colors. The mineral Chalcedony is usually thought of as an individual mineral, but in actually it is a variety of Quartz. Chalcedony is the microcrystalline form of Quartz; agates and jaspers fall under this category of Chalcedony.

Quartz can be divided into two groups based on their appearance: crystallized and microcrystalline. Crystallized are the well-formed crystals which can be easily seen. Micro crystals cannot be seen by the unaided eye. The presence of impurties in crystallized quartz can change the color of these crystals, such as amethyst, citrine, smokey quartz, rose quartz, and milky quartz are all the well-formed quartz crystals. Tiger eye is a quartz that contains fibers of asbestos giving it the sheen that is commonly associated with tiger eye stones. Pure quartz crystals are colorless. Some of the highest quality crystals can be found here the United States in the state of Arkansas.

The microcrystalline version of quartz is called Chalcedony which includes stones such as agates, jaspers, chert, flint. Carnelian is a chalcedony which is a red to orange color due to the presence of iron oxides. Chrysoprase, a green color is also a chalcedony, and is green because of the presence of nickel oxide. When chalcedony is banded it is called an agate.

Colorless Quartz Crystals, United State, Arkansas

Smoky Quartz

Amethyst Quartz, Brazil

Citrine Quartz, Brazil

Aqua Aura Cactus Quartz, South Africa

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