CRONUSITE, Ca_(0.2)(H_2O)_2CrS_2, A NEW MINERAL FORM THE NORTON COUNTY ENSTATITE ACHONDRITE

摘要

Cronusite is accessory mineral in Norton County meteorite (enstatite achondrite) Ii occurs as grains up to 1 mm disseminated in enstatite. Associated minerals: ferroan alabandite, troilite, daubreelite. Colour coal black. Streak black. Luster submetallic. Opaque. Mohs' hardness 1.5. Cleavage perfect on {001}. D_(meas) 2.51(3), D_(calc) 2.55(1) g/cm~3. In reflected light cronusite is grey. Birefringence strong pleochroism in grey colours. Anisotropy strong in grey colours. R_(max)/R_(min) (#lambda#) in air (percent): 15.4/14.2(440), 15.8/14.5(460), 16.4/14.7(480), 16.8/15.0(500), 17.2/15.4(520), 17.6/15.7(540), 17.9/15.9(560), 18.2/16.2(580), 18.4/16.4(600), 18.5/16.5(620), 18.6/l6.6(640), 18.6/16.6(660), 18.6/16.7(680), 18.7/16.8(700). VHN(load 10g) 82-109 kg/mm~,2 average 98 kg/mm~2, Trigonal, R3m, R3m or R32. a_0 = 3.326, c_0=33.29 A, V_0 = 318.9(5) A~3, Z = 3 X ray powder diffraction pattern d(I)(hkl): 11.1(100)(003), 5.56(10)(006), 3.700(4)(009), 2.719(5)(104), 2.464(4)(107), 2.180(4)(1.0.l0). IR-absorption spectrrum contains the following bands: 1595, 1625, 2910, 3390 И 3575 cm~(-1). Chemical composition (electron microprobe, average of6 analyses, wt percent): Na 0.0, K 0.6, Ca 4.2, Cr 33.7, S 39.1,O 21, H 2.65 (calculated on die basis of oxygen content), total 101.25. Empirical formula based on (Cr+S) = 3: (Ca_(0.17)K_(0.52))_(0.19)Cr_(0.14)S_(1.96) centre dot 2.14H_2O. Simplified formula: Ca_(0.2)(H_2O)_2CrS_2. Cronusite is a terrestrial weathering product of caswellsilverite, NaCrS_2. It is named for one of the Titans in Greek mythology, Cronus (Greek Kpovos (kro-nos)), the son of Uranus and Gaea. The name means mixed meteoritic-terrestrial origin of the mineral.