Crystallographic study of the low-temperature dehydration products of gypsum, CaSO/sub 4/ x 2H/sub 2/O: hemihydrate CaSO/sub 4/ x 0. 50H/sub 2/O, and. gamma. -CaSO/sub 4/
The crystal structure of ..gamma..-CaSO/sub 4/ (a = 6,9694(8), c = 6.3033(4)A; Z = 3; space group P6/sub 2/22) has been refined from time-of-flight neutral powder diffraction data to agreement factors of 4.92 (weighted profile R) and 12.10 (Rietveld R). The observed neutron powder profile for hemihydrate (CaSO/sub 4/ x 0.50D/sub 2/O) is qualitatively consistent with a model in which the water molecules occupy two different levels in the channels of a distorted ..gamma..-CaSO/sub 4/ framework. Hemihydrates formed by dehydration of gypsum (CaSO/sub 4/ x 2H/sub 2/O) or synthesized from concentrated solutions of HNO/sub 3/ are monoclinic with space group I2 (a = 12.062(4), b = 12,660(3) c = 6.930(1)A; ..gamma.. = 90/sup 5/). Experimental data do not support the existence of a high-temperature trigonal form. Hemihydrate crystals grown in saturated NaCl solution contain ca 0.50 wt.% Na/sub 2/O. The presence of Na stabilizes the structure and produces significant changes in the refractive indices and unit-cell parameters. 24 references, 7 figures, 3 tables.
- Research Organization:
- Univ. of Louisville, KY
- OSTI ID:
- 6961889
- Journal Information:
- Am. Mineral.; (United States), Journal Name: Am. Mineral.; (United States) Vol. 69:9-10; ISSN AMMIA
- Country of Publication:
- United States
- Language:
- English
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580100* -- Geology & Hydrology-- (-1989)
ALKALINE EARTH METAL COMPOUNDS
ANHYDRITE
CALCIUM COMPOUNDS
CALCIUM SULFATES
CRYSTAL STRUCTURE
DEHYDRATION
GEOLOGIC DEPOSITS
GYPSUM
HYDROGEN COMPOUNDS
MINERALS
OPTICAL PROPERTIES
ORIGIN
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
REFRACTIVITY
SEAWATER
SULFATE MINERALS
SULFATES
SULFUR COMPOUNDS
SYNTHESIS
WATER