C A L 



valleys, and at the bottom of lakes, 

 by a process which bears some 

 resemblance to chemical formations. 

 Springs containing carbonic acid, 

 that issue from limestone strata, 

 contain particles of carbonate of 

 lime chemically dissolved in water; 

 but on exposure to air and light, 

 the carbonic acid, which had but a 

 slight affinity for the particles of 

 limestone, separates, and the parti- 

 cles of lime are precipitated, and 

 form calcareous in crustations : these, 

 in the course of time, form beds, 

 and occasionally are of sufficient 

 hardness to be used for architectural 

 purposes. Thermal springs holding 

 in solution calcareous earth, rapidly 

 deposit beds of calcareous tufa. 

 At a temperature of 60 Fah., lime 

 is soluble in 700 times its weight 

 of water; if to this solution a small 

 quantity of carbonic acid be added, 

 a carbonate 'of lime is formed, and 

 precipitated in an insoluble state. 

 If, however, the carbonic acid be 

 in such quantity as to supersaturate 

 the lime, it is again rendered solu- 

 ble in water ; and it is thus that 

 carbonate of lime, held in solution 

 by an excess of fixed air, not in 

 actual combination with the lime, 

 but contained in the water, and 

 acting as a menstruum, is commonly 

 found in all waters. Hence it is 

 obvious, that a deposition of car- 

 bonate of lime from water may be 

 occasioned by either an absorption 

 of carbonic acid, or from the loss of 

 that portion which exists in excess. 

 CALC-DIABASE, A finely-grained, or 

 entirely compact diabase, with round 

 grains of calc-spar. 



CALCE'DONY. } (calcedonius, Lat. calce- 

 CHALCE'DONY. ) doine, Fr. calcedonia, 

 It. Sometimes spelt chalcedony.) 

 The Gemeiner Kalzedon of "Werner. 

 Quartz agathe calcedoinoe of Haiiy. 

 Silox calcedoine of Brongniart. A 

 semi-transparent and translucent 

 variety of quartz, to which this 

 name has been applied, from its 



[ 66 ] C A L 



having been formerly found at 

 Calcedon. It is a simple, siliceous, 

 uncrystallized mineral. Flint nod- 

 ules are frequently calcedonic, the 

 calcedony occupying the hollows of 

 such flints, and being either mam- 

 millated, botryoidal, or stalactitical. 

 It has been observed that although, 

 in the present compact state of the 

 matter of flint, it is not easy, 

 though possible, to force a fluid 

 through its pores, yet it is probable 

 that before its consolidation was 

 complete, it was permeable to a 

 fluid whose particles were finer 

 than its own ; and that the particles 

 of calcedony, while yet in a fluid 

 state, being finer than those of 

 common flint, did thus pass through 

 the outer crust to the inner station 

 they now occupy ; and that these 

 particles of calcedony permitted a 

 passage through their interstices to 

 the finer particles of still purer 

 siliceous matter which, in the form 

 of crystallized quartz, are often 

 found crystallized in the centre, 

 enveloped both by calcedony and 

 common flint. "When flints contain 

 calcedony, there may generally be 

 perceived some small bubbles, or a 

 mammillated appearance, in some 

 part of the exterior of the flint: 

 between calcedony and flint there 

 is a near resemblance, being only 

 different modes of the same sub- 

 stance. Specific gravity 2*56. 

 There are several sub-species ; the 

 beautiful apple-green is called 

 chrysoprase; the grass-green va- 

 rieties, plasma; those with red, 

 brown, yellow, and green tints, 

 carnelian ; others are known as 

 heliotrope, jasper, onyx, agate, &c.; 

 these will all be described under 

 their several names, and in their 

 proper order. Of common calcedony 

 the most usual colour is grey, passing 

 into blue and brown by every in- 

 termediate variety. It is harder 

 than flint, and infusible before tho 

 blow-pipe without addition. When 



