Bulletin of the National Speleological Society - ISSN 0146-9517
Volume 24 Part 2: 88-94 - July 1962

A publication of the National Speleological Society

Hexagonal Stalactite from Rushmore Cave, South Dakota
William A. Bassett and Allen M. Bassett

Abstract

A stalactite having the form of a hexagonal prism was found in Rushmore Cave near Rapid City, South Dakota. The broken end is a cleavage plane inclined to the axis of the stalactite indicating that the stalactite is a single crystal of calcite. The dimensions of the stalactite and the pattern revealed in the cleavage face suggest that it formed as a monocrystalline soda straw which served as a seed crystal for subsequent calcite deposition on the exterior. Two soda straw stalactites from the Ohio Caverns, West Liberty, Ohio were found to be monocrystalline with their c-axis vertical. A soda straw grows at its tip by the deposition of CaCO3 from the drop hanging there. It is suggested that in soda straws calcite's rapid growth in the c direction favors domains with vertical c-axes because they grow rapidly into the drop and eliminate domains having different orientations.

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