LIME. 



473 



being either columnar, in which the individuals are 

 straight, parallel, or diverging, and often of remark- 

 able delicacy; or the composition is granular, the 

 individuals being of various sizes, and even impalp- 

 able. The individuals, in these varieties, cohere 

 more or less firmly. If the composition be impalp- 

 able, the fracture becomes splintery, uneven, flat, 

 conchoidal, or even; on a large scale, it is sometimes 

 scaly. The fracture is earthy in those varieties in 

 which the individuals cohere but slightly. The 

 breaking up of this species into sub-species and 

 varieties, which was practised by the older writers 

 on mineralogy, and which has left us numerous par- 

 ticular denominations, and no little confusion, re- 

 quires notice in this place. These distinctions, it 

 will be seen, depended chiefly upon the mode of 

 composition, and upon admixtures and impurities 

 with which the individuals have been affected during 

 their formation. Of these, limestone represents the 

 greater part of the pure varieties of the species. 

 The simple varieties, and those compound ones in 

 which the individuals are of considerable size, and 

 easily cleavable, have been called calcareous spar 

 compound varieties of granular, still discernible 

 individuals, are granular limestone; both compre- 

 hended under the head of foliated limestone. If the 

 granular composition disappear, compact limestone is 

 formed, under which denomination the oolite, or roe- 

 stone, was comprehended. The roundish grains, how- 

 ever, of the latter, consist of columnar individuals, 

 disposed like the radii of a sphere, and frequently 

 showing distinct traces of cleavage. Common fibrous 

 limestone is produced by columnar composition, in 

 massive varieties; the fibrous calcsinter, by the same, 

 but appearing in various imitative shapes. Peastone, 

 or pisolite, consists of diverging columnar indivi- 

 duals, collected into curved lamellar ones, forming 

 globular masses, which are again agglutinated by a 

 calcareous cement. Each of the globules, generally, 

 contains a fragment of some heterogeneous matter, 

 as quartz, granite, &c. Compact limestone passes 

 into chalk, when the individuals are more loosely 

 connected with each other, so that the whole assumes 

 an earthy appearance; and rock milk, or agaric mine- 

 ral, is formed, if the mass contains so many interstices 

 that it seems to possess but a small degree of specific 

 gravity. Calcareous tufa, a recent deposit, formed 

 on the surface of the earth, is often cleavable, and thus 

 possesses all the properties of calcareous spar. Slate 

 spar is produced by a lamellar composition, in mas- 

 sive varieties, and often exhibits a pearly lustre. 

 Stvinestone, anthracolite, marl, and bituminous mar- 

 lite are impure and mixed varieties, partly of calcar- 

 eous spar, partly of compact limestone. The pure 

 varieties of rhomboidal limestone consist of lime, 56, 

 and carbonic acid, 43. Very often, the varieties con- 

 tain variable proportions of oxide of iron, silica, 

 magnesia, alumine, carbon, or bitumen. If pure, it 

 is entirely soluble in nitric acid, during which a brisk 

 effervescence takes place. In the common fire, it is 

 infusible, but loses its carbonic acid, and becomes 

 burned, or quicklime. Limestone rarely enters into 

 the composition of rocks : in most cases, the more 

 considerable masses of it form particular beds in 

 other rocks, or constitute rocks themselves ; the 

 latter consist chiefly, though not exclusively, of 

 compact limestone ; the former of granular lime- 

 stone. The simple varieties occur in drusy cavities, 

 more frequently in veins than in beds, accompanied 

 with the varieties of different species. Calcareous 

 tufa and rock-milk, being of a sintery formation, 

 occur upon the surface, and in fissures of limestone 

 rocks. Stalactitic and pisiform varieties are pro- 

 duced by calcareous springs and other waters. The 

 mixed, or impure varieties occur in particular strata, 



between those of compound varieties of other species. 

 It very often occurs in petrifactions, imbedded in 

 compact varieties of the same species. Rhomboidal 

 limestone, as has already been remarked, is a species 

 very widely diffused in nature ; several of its varie- 

 ties have a considerable share in the constitution of 

 mountains, in many countries. This is particularly 

 true in Switzerland, Italy, Carniola, Carinthia, Salz- 

 burg, Stiria, Austria and Bavaria, and in several parts 

 of America. Of crystallized varieties, the most re- 

 markable occur in Derbyshire and Cumberland, in the 

 mining districts of Saxony and Bohemia, in the Uartz, 

 in Carinthia, Stiria, Hungary and France, and, in the 

 United States, at Lockport in New York, forming 

 geodes in compact limestone. Iceland is the locality 

 of the purest and most transparent varieties, from 

 whence come the best pieces of the doubly-refracting 

 spar. The crystallized sandstone of Fontainebleau, 

 in France, is a variety of rhomboidal limestone, 

 mechanically mixed with sand. Slate-spar occurs 

 in Saxony, Norway and Cornwall. Pisolite is found 

 in Carniola, and at Carlsbad in Bohemia. Most of 

 the varieties are so common as to render the mention 

 of their localities unnecessary. Several varieties of 

 the present species are usefully employed for various 

 purposes, partly depending upon their mechanical, 

 partly upon their chemical composition. Those used 

 in sculpture and in ornamental architecture, are 

 called marble; the more common or coarse varieties 

 are used for the common purpose of building ; a 

 peculiar variety of very fine-grained compact lime- 

 stone is used for plates in lithography. The best 

 sort is found near Pappenheim and Sohlenhofen, in 

 Bavaria. Quicklime mixed with sand and water 

 forms mortar. Carbonic acid, for chemical pur- 

 poses, is often obtained from chalk or marble pow- 

 der. It is also a valuable addition in several pro 

 cesses of melting ores, and in producing certain 

 kinds of glass. There is another species, in mineral- 

 ogy, called Arragonite, which was formerly con- 

 founded with that just described. In composition, 

 it is scarcely distinguished from rhomboidal lime- 

 stone, the most accurate analysis having been unable 

 to make known more than from 5 to4'l of carbonate 

 of strontites in its composition, besides carbonate of 

 lime. Its crystallization, and other characters, how- 

 ever, sufficiently characterize it as distinct from lime- 

 stone. It occurs in crystals, which, at first sight, 

 appear to be regular six-sided prisms ; but a close 

 inspection will discover a longitudinal crevice down 

 each lateral face, and somewhat similar appearances 

 converging in the centre of the terminal planes. It 

 also occurs in prismatic crystals, of four or six sides, 

 terminated by planes, the prisms often being so short 

 as to impart to the crystal the general form of an 

 octahedron ; these are rarely separate, but mostly 

 cross each other at particular angles. Its crystals 

 yield to mechanical division, parallel to the lateral 

 planes of a right rhombic prism of 116 5' and 63 

 55', by measurement taken with the reflective 

 goniometer, on cleavage planes. Lustre vitreous, 

 inclining to resinous, upon faces of fracture ; colour 

 white, sometimes passing into gray, yellow, or 

 mountain green ; transparent or translucent ; brittle; 

 hardness such as to scratch calcareous spar ; specific 

 gravity, 2 93. It is very liable to occur in globular, 

 reniform, and coralloidal shapes, and massive, with 

 a columnar composition. Imbedded crystals, gener- 

 ally twins, or consisting of a greater number of indi- 

 viduals, are found in compound varieties of gypsum, 

 mixed and coloured with oxide of iron, accompanied 

 with crystals of ferruginous quartz. Other varieties 

 occur in the cavities of basalt and other trap rocks, 

 in lavas, also in irregular beds and veins. It is 

 found in beds of iron ores, in those coralloidal 



