The occurrence of monohydrocalcite in two small lakes in the south-east of South Australia

Graham F. Taylor

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Research Article| August 01, 1975

The occurrence of monohydrocalcite in two small lakes in the south-east of South Australia

Graham F. Taylor

CSIRO, Division of Mineralogy, P.O. Box 136, North Ryde, New South Wales, Australia, 2ll3

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Author and Article Information

Graham F. Taylor

CSIRO, Division of Mineralogy, P.O. Box 136, North Ryde, New South Wales, Australia, 2ll3

Publisher: Mineralogical Society of America

Received: 01 Oct 1974

Accepted: 05 Mar 1975

First Online: 11 Jul 2018

Online ISSN: 1945-3027

Print ISSN: 0003-004X

Mineralogical Society of America

American Mineralogist (1975) 60 (7-8): 690–697.

Abstract

Monohydrocalcite is the main constituent of beach rocks surrounding Lakes Fellmongery and Butler near Robe in the south-east of South Australia. It occurs as hard pelletal aggrigates with a sponge-like texture which resembles calcareous tufa.

At Lake Fellmongery, it appears that the monohydrocalcitie is formed in saline waters with high Mg/Ca ratio, high pH, and in the presence of blue-green algae. Isotopic data suggest that the monohydrocalcite is not secreted by the algae but rather that it is precipitated from saline waters.

The composition of monohydrocalcite derived from the most comprehensive chemical analysis is (Ca_0.9053 Mg_0.0788 Fe_0.0022 Sr_0.0047 Na_20.0133 K_20.0008)CO₃ · l.15H₂O. All the water is firmly bound in the crystal structure, which appears to be stable when dry, but transforms in water to calcite.

X-ray powder diffraction data have been indexed on a hexagonal unit cell containing 9 (CaCO₃ · H₂O) and yield lattice parameters of a = 10.566Å, c = 7. 573 Å. The strongest reflections are: 4.333 100; 3.078 70; 1.9308 65; 2.829 50; 2.1665 45; 5.283 35.