Selenium APEX Mineral

Selenium (Se #34) is the next element on the periodic table for my APEX mineral collection. 

Wikipedia Selenium

Selenium Minerals - There are lots of minor Selenium minerals.  

Penroseite ((Ni,Co,Cu)Se2) with 73% Selenium is my obvious APEX mineral. It can be found as inclusions in other minerals. The dark areas above are Penroseite.   It is a trash can mineral where various elements can substitute into the main selenide (Se2) matrix.  Pure selenides (e.g. NiSe2) are extremely rare.  

Selenium exists as several allotropes that interconvert upon heating and cooling.  Each form has very different chemical properties with other elements.

• Amorphous, brick-red powder 
• Black, vitreous form sold as beads
• Gray crystal form is most stable

Selenium and its compounds were unknown before modern times.

Selenium is usually produced as a byproduct of Copper refining.  Only 2,000 tons are produced each year.  Most Selenium is used in glass production to confer a red color.

Selenium is necessary for a variety of enzymes in animals. It is concentrated in large amounts in some plants.   which have been known to poison animals .  Animals can be poisoned by eating large amounts of Selenium containing plants called "locoweeds".