Vesuvianite is a calcium-bearing silicate mineral. It occurs typically in impure metamorphosed carbonate rocks (silicate marble) and skarns.
It is usually green, brown, or yellow and also known by the name idocrase. It is usually associated with other calc-silicate minerals like diopside, garnets, wollastonite, etc. It may occur in alkaline igneous rocks (nepheline syenite) and in metamorphosed mafic dikes, which also contain serpentine, garnet (grossular), diopside, and epidote. Garnet and vesuvianite-bearing metamorphosed mafic igneous rocks are called rodingites.
The color of the mineral is mostly controlled by the amount of oxidation state of iron and titanium. Cyprine is a bluish Cu-bearing variety. Californite is an olive green variety, known also as American jade or California jade because of jade-like appearance.
Vesuvianite may strongly resemble grossular (garnet group mineral). Both of these minerals occur in silicate marbles.
Vesuvianite is a relatively common mineral, but only in cerain rocks, which have a rather restricted occurrence. Overall, it is an uncommon mineral species and considered to be one of the so-called rock-forming minerals only because it is a noteworthy phase in some rocks.
Crystal (6 cm) with garnet in a skarn from Kristiansand, Norway. TUG 1608-4632