CALK, a genus of minerals, which is divided into twenty species. 1. Rock milk, denominated, by Werner, berg milch. 2. Chalk, denominated kreide, or creta alba : external characters : co lour white: occurs massive disseminated, and as a crust covering flint ; fragments indeterminately angular, blunt edged ; opaque; soils ; writes ; easily frangible ; specific gravity according to Kirwan 2.3, hut bishop Watson takes it at 2.6; vari ous specimens will no doubt account for this and other differences of the same kind. It effervesces strongly with acids, and is found to consist almost entirely of lime and carbonic acid. It constitutes a peculiar kind of formation; contains nu merous flinty petrifactions ; and is even remarkable for being the most general repository of flint, It is found chiefly on sea-coasts, as at Calais and Dover, and several of the Danish islands in the Bal tic, as Rugen and Zealand : it occurs also in Poland; and several great tracts of country in the south of England are corn. posed of it. In some parts of Kent a chalk pit is no contemptible estate, pro ducing from one to five hundred per annum and upwards. In the manufac tures it is used for polishing and cleansing metals, &lass, &c. and when burnt into lime, it is of great importance in build ing. 3. Lime-stone ; denominated kalk stein, which is divided into four sub species, viz. compact-limestone ; foliated lime-stone ; fibrous limestone ; peastone. The first is of a greyish colour, com posed chiefly of lime and carbonic acid, with small portions of iron, alumina, and inflammable matter ; and is found in the sandstone and coal formations of Saxony, Bohemia, Bavaria, Sweden, France, Eng land, Scotland, &c. It is used as mor tar, when deprived of its carbonic acid, and in this state also it is employed in the manufiicture of soap, in tanning, and other processes. It is likewise used as a flux, in the reduction of such ores as are difficultly fusible, by means of its silica and alumina. The Florentine arbo
rescent marble, a variety of this species, is, according to Jameson, very valuable for the purposes of ornament ; and the limestone of Pappenheim serves for pay. ing, grave-stones, and sometimes for po lishing plate-glass. Of the foliated lime stone, the granular is the most important variety : this is purer than common lime stone, is found peculiarly beautiful at Carrava in Italy, where it is quarried, and from thence distributed over Europe, for the purposes of statuary. The white marble of Paros has been long celebrated for its fitness for sculpture, and other useful purposes. Cale-spar is another variety, of which many of its most beau tiful and rare crystallizations are found in Derbyshire, in Ireland, and many parts of the continent. The fibrous limestone occurs only in small veins : the satin spar of Derbyshire belongs to this kind. The calc•sinter is a variety of the fibrous limestone, of which there is a striking instance in the grotto of Anteparos when it occurs in large masses, it is used by the statuary for many of the pur poses of marble. The alabaster of the ancients is calk-sinter. It was brought from Arabia in considerable quantities, and used principally for the drapery of marble statues. Peastone is found in great masses in the vicinity of the hot springs at Carlesbad in Bohemia. Parti cles of sand appear to be raised in the water by means of air-bubbles, and be come covered with calcareous earth, which is deposited around them in lamel lar concretions of the size of a pea ; hence the name. 4. Schaum earth, or foaming earth, found in the neighbour hood of Gera, in the forest of 'Thurin gia; also in the north of Ireland : it is called by Werner Schaumerde, and is thought by him to be nearly allied to slate spar, which is another species, com posed almost entirely of carbonate of lime. The remaining species we pass over as of less interest.