Variation of gypsum morphology along deep core SG-1, western Qaidam Basin (northeastern Tibetan Plateau) and its implication to depositional environments

The lattice parameters of the unit cell of gypsum, measured by X-ray diffraction method, are: a = 5.854-12.57 Å; b = 9.654-16.231 Å; and c = 5.163-14.024 Å; β = 113.54-119.88°; Volume = 601.55-712.65 Å3. The substitution of K+, Na+ and Mg2+ for Ca2+ can reduce c-axis, while Sr2+ can reduce a and b axes. a/c, b/c, a/b tend to increase with K+, Na+ and Mg2+ and decrease with Sr2+. The Mg2+, Na+, K+ and Sr2+ contents in gypsum show significant variability, with K/Ca molar ratios varying from 1.03 × 10−4 to 32.08 × 10−4, Mg/Ca molar ratios from 0.0023 to 0.1629, Na/Ca molar ratios from 0.031 to 0.575, and Sr/Ca molar ratios from 5.59 × 10−4 to 19.67 × 10−4. Sr2+, Mg2+, Na+, and K+ concentrations in gypsum mainly depend on growth rate and brine concentration.