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ne affords us also a touchstone for the trial of spirits. South. Irish touchstone (Min.), basalt, the stone which composes the Giant's Causeway.

dark- colored, heavy igneous rocks, including especially the feldspathic- augitic rocks, basalt, dolerite, amygdaloid, etc., but including also some kinds of diorite. Called also trap rock. Trap tufa, Trap tuff, a kind of fragmental rock made up of fragments and earthy materials from trap rocks.

which have been produced from the discharges of volcanic matter, as the various kinds of basalt, trachyte, scoria, obsidian, etc., whether compact, scoriaceous, or vitreous.

A soft, earthy, dark-colored rock or clay derived from the alteration of basalt.

A provincial name given in England to basaltic rocks, and applied by miners to other kind of dark-colored unstratified rocks which resist the point of the pick. -- for example, to masses of chert. Whin-dikes, and whin-sills, are names sometimes given to veins or beds of basalt.

ndite, and others. These species occur of secondary origin in the cavities of amygdaloid, basalt, and lava, also, less frequently, in granite and gneiss. So called because many of these species intumesce before the blowpipe. Needle zeolite, needlestone; natrolite.