Hydrogrossular is a calcium garnet series (formula: Ca3Al2(SiO4)3−x(OH)4x, with hydroxide (OH) partially replacing silica (SiO4)). The endmembers of the hydrogarnet family (grossular ) depend on the degree of substitution (x): * grossular: x = 0 * hibschite: 0.2 < x < 1.5 * katoite: 1.5 < x < 3.
Hydrogrossular is a garnet variety in which a Si4+ is missing from a tetrahedral site. Charge balance is maintained by bonding a H+ to each of the four oxygens surrounding the vacant site.
Hydrogrossular is found in massive crystal habit , sometimes grown in with idocrase
Hydrogrossular is translucent , and found in green to bluish green, pink, white, and gray. The cause of the green color is chromium. Pink hydrogrossular is caused by the presence of manganese. Hydrogrossular may have dark gray to black small inclusions., and has the misnomers
Hydrogrossular is sometimes used as a gemstone , being cabochon. Sources for green and pink hydrogrossular are South Africa , and the United States. White hydrogrossular is sourced from Burma