Abstract
A CURIOUS formation is described by Mr. E. Goldsmith in the Proceedings of the Philadelphia Academy of Natural Sciences (part i. 1894, p. 107). It is well known that the highly heated and very fluid lava in the Kilauea crater at Hawaii, as well as in other craters, is occasionally shot up into the air some thirty feet or more. This lava in its descent through the air becomes very porous. If such a highly porous rock have a space underneath, a fresh deposit of liquid lava will trickle through the porous cooled lava, forming as it solidifies the pendant stalactites shown in the accompanying picture, which illustrates Mr. Goldsmith's paper, and has been kindly sent to us by the Academy. The figure represents the entrance to a volcanic cave, photographed by Profs. Sharp and Libbey. It shows an overhanging roof of porous basalt, from which are suspended irregularly gnarled rods ot volcanic stalactites; on the floor are scattered fantastic-shaped volcanic stalagmites, which seem to be much thicker than the pendant rods above. Mr. Goldsmith says that the stalactites are about one-fourth of an inch thick, and about eight inches long. They show no disposition to form cones like those seen in limestone caves. They are mostly hollow and porous, and very brittle. The colour is usually a deep black, but sometimes a part is of a brownish tint, due, Mr. Goldsmith thinks, to a higher oxidation of the magnetite present. Fragments of the stalactites, when microscopically examined, exhibited a glassy felspar having apparently the Characteristic of sanidine. Magnetite occurred in great profusion, and also gases, probably air. Augite was suspected, but not definitely determined. The specific gravity of a coarse powder produced from the stalactites was found to be 2˙85. The lava is decidedly basic, as the quantity of silica determined analytically was 48˙55 per cent. On some of the stalactites a thin layer of colourless crystals were recognised under the microscope. An examination of these incrusting crystals proved them to be selenite.
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Volcanic Stalactites. Nature 51, 128–129 (1894). https://doi.org/10.1038/051128b0
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DOI: https://doi.org/10.1038/051128b0