The chemical formula for benitoite is BaTiSi3O9. The mineral is thought to have been derived from the surrounding wall rock during a phase of low temperature and high-pressure metamorphism which relates to a blueschist metamorphic facies. The elements that comprise benitoite are thought to have been mobilized from the host rock and deposited in a late stage cooling of hydrothermal fluids in veins fracturing the wall rock of serpentine. Van Baalen, 1995, suggests that the benitoite mineralization was subsequent to the formation of the blueschist. His analysis places the age of the blueschist at between 100 and 160 million years of age and the benitoite present in the cross cutting veins at 12 million years. All benitoite found at the Benitoite Gem mine is confined to blueschist rocks. The last phase of mineralization was confined to natrolite that was injected into the vein system. It is found to encase most, but not all, of the minerals deposited in the earlier phases.