Merrihueite, A New Alkali-Ferromagnesian Silicate from the Mezö-Madaras Chondrite

Merrihueite, a new mineral with the approximate chemical composition (K,Na)(2)(Fe,Mg)(5)Si(12)O(30), occurs with iron-rich olivine, iron-poor pyroxene, and nickel-iron in a few chondrules of the Mezö-Madaras chondrite. The refractive index lies between 1.559 and 1.592; the birefringence for each composition is low to moderate. X-ray powder data for merrihueite are nearly identical to those for osumilite, (K,Na,Ca)(Mg,Fe)(2)(Al,Fe)(3)(Si,Al)(12)O(30)-H(2)O, and very similar to those for synthetic K(2)Mg(5) Si(12) O(30). Merrihueite is interpreted as an alkali-ferromagnesian silicate mineral of the osumilite type. It is named in honor of the late Craig M. Merrihue, meteoriticist, of the Smithsonian Astrophysical Observatory.