Selenium, pure hexagonal

In the native condition the element is occasionally found as hexagonal prismatic crystals, which are nearly pure. The foreign metals present, usually only in small quantity, may be gold, silver, copper and iron. Free tellurium is also present to the extent of approximately 0-17 per cent, in the red sulphur of Japan, which also contains about 6 per cent, of selenium and 1 per cent, of arsenic.8 Traces of tellurium may be found in Spanish pyrites.9... 

Selenium is a naturally occurring, solid substance. It is widely but unevenly distributed in the earth s crust. It is commonly found in rocks and soil. Selenium, in its pure form of metallic gray to black hexagonal crystals, is often referred to as elemental selenium or selenium dust. 

Pure selenium, like sulfur, is allotropic, and exists in three forms a gray hexagonal form, a red monoclinic form, and a vitreous amorphous form. All forms can exist at room temperature and one atmosphere, but only the hexagonal form is thermodynamically stable [53]. 

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