New data on hungchaoite, the second world occurrence, Death Valley region, California

Hungchaoite occurs with ginorite, mcallisterite, sborgite, sassolite, nobleite, ulexite, and, where gypsum and ulexite are abundant, with kurnakovite, inderite, and mcallisterite in surficial matrix as products from weathered colemanite and priceite veins in late Tertiary rocks.

Hungchaoite is triclinic, space group P1; a = 8.811(1), b = 10.644(2), с = 7.888(1)A; α = 103°23(1)′, β = 108°35(1)′, γ = 97°09(1)′ unit-cell volume 666.2(1)A³; Z = 2[MgO·4B₂O₃·9H₂O]. Euhedral, tabular {100} to equant, colorless, untwinned crystals, up to 0.5 mm, show 17 forms. The strongest lines in the X-ray powder pattern are, in A: 6.71(100), 3.356(92), 5.36(85), 4.093(78), 4.079(64), and 7.14(59).

Hungchaoite is optically (−): α = 1.445(2),β = 1.485(2), γ = 1.490(2) (Na light); 2V_α = 15(4)°; r < υ, distinct; X∧ a = +28°, Z∧ b = +37°, Y∧ c = −66°. Good {111} and {111}and imperfect {010} cleavages. Hardness 2½. G (meas) 1.706(5), ρ (calc) 1.705 g cm⁻³.

Hungchaoite is metastable with respect to inderite and mcallisterite in solution. Dehydration data are given.