49 f- CALC GENUS. Fracture almoft always perfectly foliated, moft commonly flraight foliated, feldom fpherically curved foliated. It {hews a threefold cleavage. Sometimes lias a concealed foliated fraUure. Fragments rhomboidal. r I he maflive occurs in very large and coarfe grain ed diftincl concretions, feldom fmall grained; alf<? in thick and thin prilmatic diveiging and in- terfecling concretions, which are obliquely longitudi nally ftreaked ; alfo in wedge-fhaped pritmatic con* cretions, which are alfo deeply and obliquely ftreaked- 1 he maftive varieties areVanflucent, and l'ometinies even tranfparcnt. Cryftals tranfparent and fenjitranf' parent, The tranfparent varieties are alfo duplicating* Semi-hard, Brittle. Very cafily frangible. Not particularly heavy. Specific gravity.—3,70c. Conflituent Parts. It is ccmpofed of lime and carbonic acid in proportion of 35 to 34 in the hundred. Its water of cryftallizaticn is very inconfiderable, being, according to Bergman, in the 100 parts.