Vesuvianite or "idocrase", comes in several colors.   It can have many impurities which lend to it's color, the most common impurities are iron, magnesium, water, and boron.

They can be green, brown, yellow, or even blue, high quality faceted stones make valuable gemstones. 

The specific gravity is 3.4 and the Mohs hardness is 6+1⁄2. The name "vesuvianite" was given by Abraham Gottlob Werner in 1795, because fine crystals of the mineral are found at Vesuvius; these are brown in color and occur in the ejected limestone blocks of Monte Somma. Several other names were applied to this species, one of which, "idocrase" by René Just Haüy in 1796, is now in common use.

A sky bluish variety known as cyprine has been reported from Franklin, New Jersey and other locations; the blue is due to impurities of copper in a complex calcium aluminum sorosilicate. Californite is a name sometimes used for jade-like vesuvianite, also known as California jade, American jade or Vesuvianite jade. Xanthite is a manganese rich variety. Wiluite is an optically positive variety from Wilui, Siberia. Idocrase is an older synonym sometimes used for gemstone-quality vesuvianite. Also, Vessonite and Vassolite are variant spellings commonly encountered in the gem trade.