benstonite

{{Infobox mineral | name = Benstonite | category = Carbonate minerals | image = Benstonite-Calcite-Fluorite-154901.jpg | imagesize = 260px | alt = | caption = Benstonite with calcite | formula = Ba6Ca6Mg(CO3)13 | IMAsymbol=Ben | molweight = | strunz = 5.AB.55 | dana = 14.2.3.1 | system = Trigonal | class = Rhombohedral () H-M group: () | symmetry = R | unit cell = a = 18.280 Å, c = 8.652 Å; Z = 3 | color = Snow-white, ivory, very pale yellow, pale yellowish brown | habit = | twinning = | cleavage = Good on {312} | fracture = | tenacity = | mohs = 3–4 | luster = Vitreous | polish = | refractive = nω = 1.690 nε = 1.527 | opticalprop = Uniaxial (−) | birefringence = δ = 0.163 | 2V = | dispersion = | pleochroism = | fluorescence= Red or yellow under UV and X-rays | absorption = | streak = White | gravity = | density = | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = Translucent | other = | references = }} Benstonite is a mineral with formula Ba6Ca6Mg(CO3)13. Discovered in 1954, the mineral was described in 1961 and named after Orlando J. Benston (1901–1966).

==Description and occurrence== Benstonite is translucent and white, pale yellow, or pale yellow-brown in color. The mineral occurs as cleavable masses; cleavage fragments are nearly perfectly rhombohedral in shape. Cleavage faces are up to across and slightly curved. On large specimens, the faces exhibit a mosaic structure similar to that in some specimens of dolomite and siderite. Benstonite fluoresces red or yellow under x-rays and longwave and shortwave ultraviolet. The mineral also exhibits strong red phosphorescence.