FLINT. The true native place of this well known mineral is the upper bed of the chalk formation, where it occurs in regular beds. Gravel consists principally of flints which have been rounded by attrition, and, by exposure to air and moisture, have acquired a yellowish red colour.
Flint is usually of a gray colour. It is rather harder than quartz ; thin fragments of the black varieties are translucent ; it is fra gile, and, being rarely laminated, it is broken with equal facility in almost every direction. Specific gravity, 2.594. It is infusible, but becomes opaque and white by the action of heat. Flint is almost wholly pure silica.
The true origin of flint—as it occurs in the chalk of Europe especially—has been, and still is, the subject of much discussion among microscopists and geologists. Mr. Bowerbank believes generally in the origin of flints (and some allied minerals) from sponges. Ehren berg, finding in some flints abundance of infu sorial animalcule, suggests the origin of flint from aggregations of these silicious-shielded microzoaria.
Flint is an important article in many de partments of manufactures. In the making of glass and porcelain it is almost indispen sable ; it is the ingredient which gives hard ness and strength to those substances. Flint
glass, called by the French crystal, owes its English name to the large proportion of flint which it always contains.
Since percussion caps have been largely used in the army, gun-flints have been to the same extent abandoned ; but they used in former years to be an object of some import ance. The best chalk-flints were selected : those which occur in nodules from 2 lbs. to 20 lbs. each. Hammers of various shapes were employed in the manufacture. The workman began by holding a flint on his left thigh, and breaking it with a hammer into several broad flattish pieces. He next held one of the pieces in his left band, and chipped off the white envelope by a pointed hammer. By means of other hammers and a peculiar form of chisel he brought the pieces to the requisite size and shape for gun-flints. The gun-flint makers prided themselves on keep ing their modes of proceeding secret, at least in France and Germany.