Earth and Planetary Sciences ETDs

Publication Date

5-27-1970

Abstract

The surface energy of gypsum has been experimentally determined to be 70. 2 erg/cm2 at 30˚ C. The value for anhydrite is calculated as 112 erg/cm2. At various extrapolated supersaturations, the number of particles or ions necessary to form nuclei of gypsum and anhydrite is:

Supersaturation

No. part. or ions/nucleus

Gypsum

Anhydrite

10

60.5

1000

51

8

2

99

20

4

Crystal size measurements and crystal shapes were noted for gypsum within the range of supersaturations studied (45.6 to 131). The maximum crystal size is attained at a slightly lower supersaturation than the critical supersaturation. The shape of the gypsum crystals varies from swallow tail twins to a predominance of single crystals to microscopic rosettes with increasing supersaturation. Thick deposits of anhydrite are known in the geologic record, but only minor thin deposits are seen forming today. When calcium sulfate begins to precipitate from present sea water, the supersaturation is about 16. Hence approximately 51 particles or ions must come together and remain together to form a gypsum nucleus, while approximately 99 particles or ions are needed to form an anhydrite nucleus. It is understandable, therefore, that metastable gypsum will be the primary chemical precipitate from sea water at such low supersaturations. At high supersaturations small numbers of ions are needed to form nuclei of both gypsum and anhydrite: therefore, anhydrite has a statistically greater chance to form within its stability field. Ancient anhydrite deposits of primary origin are hypothesized to be the result of primary anhydrite precipitation from a highly supersaturated solution or the transformation of primarily precipitated gypsum to anhydrite upon coming in contact with highly supersaturated solutions in the very early diagenetic environment.

Degree Name

Earth and Planetary Sciences

Level of Degree

Masters

Department Name

Department of Earth and Planetary Sciences

First Committee Member (Chair)

Edgar F. Cruft

Second Committee Member

Lawrence A. Frakes

Third Committee Member

Abraham Rosenzweig

Fourth Committee Member

George R. Clark

Language

English

Document Type

Thesis

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