A HYDROUS CA-BEARING MAGNESIUM CARBONATE FROM PLAYA LAKE-SEDIMENTS, SALINES LAKE, SPAIN

Sediments of playa Lake Salines, SE, Spain, contain a carbonate minera l characterized by X-ray diffraction peaks very similar to, but system atically shifted from those of pure magnesite. Analyses (SEM, IR and R aman spectroscopy, DTA, TGA, and ICP) indicate the mineral is a hydrou s Ca-bearing magnesium carbonate with the chemical formula (Mg-0.92,Ca -0.08)CO3.3H(2)O. Thermal characteristics of the mineral are similar t o those of other known hydrated magnesium carbonates. X-ray and electr on diffraction data suggests a monoclinic system (P21/n space group) w ith unit-cell parameters of a = 6.063(6), b = 10.668(5), and c = 6.014 (4) Angstrom and beta = 107.28 degrees.