224 PHYSIOGRAPHY. 



Talc. 



als are sometimes strongly coherent with each other or flat, 

 so as to give rise to an imperfectly slaty structure. Often 

 earthy, without connexion of its particles. 



1. The, differences among the varieties comprehended within the pres- 

 ent species, depend upon various properties of the individuals themselves, 

 upon diversities in their composition, and Ihe presence of foreign matter. 

 The varieties of dark green (leek-green, celandine green, &c.) colors, 

 inclining to brown, constitute the chlorite,, subdivided into foliated and 

 common, slaty and earthy chlorite. The first of these contains the 

 crystallized varieties, and such compound ones as consist of easily sepa- 

 rable individuals, not presenting a slaty structure. The second contains 

 those granularly compound varieties in which the individuals can scarce- 

 ly be traced, or in which they are not observable at all. Chlorite-slate, 

 or slaty-chlorite, refers to such compound varieties as have a slaty text- 

 ure ; and earthy-chlorite to such as are but loosely coherent, or already 

 in a state of loose scaly particles. Immediately with those varieties of 

 Chlorite whose composition is impalpable, the Green Earth is connect- 

 ed ; from which, however, must be excepted what has been termed 

 crystallized Green Earth, and which, consists of decomposed crystals of 

 Pyroxene. Common Talc embraces crystallized varieties, and such 

 compound ones in which cleavage is transformed into slaty structure,. 

 the latter being generally very perfect; or such as consist of columnar 

 particles of composition. Earthy Talc, or JVacrite, consists of loose par- 

 ticles, or such as are but slightly cohering; ; Indurated Talc refers to 

 imperfect and coarse slaty varieties, in which this kind of structure is 

 more the consequence of composition than of imperfect cleavage. If 

 this structure be sufficiently imperfect to become coarse, and indistinctly 

 granular, Pot-stone, or Lapis ollaris is formed, which possessing the 

 united properlie^of softness and tenacity, may be easily turned into ves- 

 sels; for which reason only it appears to have been regarded as a dis- 

 tinct species. Closely connected with this variety, is the Steatite, which 

 often occurs in coatings and pseudomorphoses, and the soapstone, which 

 is white, or mottled red and green. 



2. Before the blow pipe, Talc offers, according to its color and foreign 

 admixtures, various appearances. In general it loses its color, and is 

 with difficulty fused, or changed into a black scoria, or is altogether infu^ 

 rible. 



