Abstract
Charlesite, ideally Ca6(Al,Si)2(SO4)2(B(0H)4)(OH,O)12·26H2O is a member of the ettringite group from Franklin, New Jersey, and is the Al analogue of sturmanite. Chemical analysis yielded CaO 27.3, Al2O3 5.1, SiO2 3.1, SO3 12.8, B2O3 3.2, H2O 48.6, sum = 100.1 percent. Charlesite is hexagonal, probable space group P31c, with a = 11.16(1), c = 21.21(2)Å. The strongest lines in the X-ray powder diffraction pattern (d, I/Io, hkl) are: 9.70, 100, 100; 5.58, 80, 110; 3.855, 80, 114; 2.749, 70, 304; 2.538, 70, 126; 2.193, 70, 226/404 Charlesite occurs as simple hexagonal crystals tabular on {0001} and has a perfect {1010} cleavage. The density is 1.77 g/cm3 (obs.) and 1.79 g/cm3 (calc.). Optically, charlesite is uniaxial (-) with ω = 1.492(3) and ϵ = 1.475(3). It occurs with clinohedrite, ganophyllite, xonotlite, prehnite, roeblingite and other minerals in several parageneses at Franklin, New Jersey. Charlesite is named in honor of the late Professor Charles Palache.