Prehnite is an inosilicate of calcium and aluminium with the formula Ca2AlSi3O12(OH) Although not classed as a zeolite, it is often found associated with minerals which are zeolites such as apophyllite, heulandite, datolite, etc. It's colour varies from light green to yellow, and may be colourless. Crystals of prehnite can be reniform, botryoidal or stalactitic. This specimen is a pseudomorph of prehnite after laumonite, in other words original laumonite has been replaced by prehnite. It's origin is only known as India, but it is probably from the Mumbai district.