Unlike tubular lava stalactites, which are extruded by escaping gases, the shark tooth stalactite grows by accretion. In most cases, as the level of flowing lava inside an active tube fluctuates, it coats protrusions on the ceiling with a thin veneer of lava. The original protrusion may have been a small driplet formed as the molten ceiling cooled. This results in a broad stalactite, usually tapering to a point. A cross section of such a stalactite will show successive layers, just as tube passages contain linings that may be several layers thick from successive flows. 
In both photos, the stalactites have been encrusted with secondary gypsum deposits.

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Created: August 4, 2000
Author: Dave Bunnell