The writer believes that a more cautious attitude should be taken toward the acceptance of much of the recent work on the use of vacuoles in geologic thermometry. Temperature determinations by the decrepitation method may be widely in error. The correction for pressure is difficult to evaluate because of the inherent errors in estimating pressure in a hydrothermal solution. Further, most corrections due to pressure that have been made in recent published papers have been considerably in error because of the inadequacy of our knowledge concerning the P-v-T relationships in water. New pressure correction curves are presented. The fundamental assumption in the use of vacuoles is challenged. Most vacuoles are present along lineage boundaries in minerals and these boundaries may serve as paths along which material may move to and from the vacuole. Experimental evidence is cited to show that material can move readily along lineage boundaries or through a crystal structure into vacuoles.

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