Abstract

Fluid inclusions in fluorite crystals were studied principally to determine the range of temperature of formation of individual crystals. Measurements were made by heating specimens and recording temperatures at which vapor bubbles within the inclusions disappeared. Over-all accuracy, excluding pressure corrections, was of the order of ±2.5° C.

Some of the fluid inclusions are arranged in geometrically regular planes parallel to cube faces. These are apparently of primary origin. Others form bands along former fractures which approximately parallel the cleavage directions and which cut across each other and the primary planes alike. Historically such inclusions have been called “secondary” although “subsequent” is considered a more meaningful designation. Most of the primary inclusions are smoothly rounded and contain petroleum, whereas “subsequent” inclusions range from jagged to smooth in outline and contain principally a clear fluid.

Measurements on primary inclusions indicate that temperatures at which the crystals grew generally ranged from 83° to 115° C., with a mean around 100° C. Commonly the indicated growth temperature increased slightly for some distance outward from the crystal center and then dropped off toward the exterior. Measurements on subsequent inclusions gave results in the range of 112° to 172° C., generally higher than those shown by primary inclusions.

Incomplete bulk analyses of the fluid from inclusions, probably mostly of the subsequent variety, show a preponderance of Ca, Na, and Cl ions, and a total concentration of dissolved material amounting to 45,000 parts per million.

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