Earths. 193 



knife, which do not effervesce with acids, and 

 suffer little or no change in the fire. They are 

 distinguished from flints by their softness ; from 

 lime, by not effervescing ; from gypsums, by not 

 calcining into plaster ; and from clays, by not 

 having the same qualities with respect to water. 

 The appearance of talc is that of a foliated stone, 

 slippery and unctuous to the touch. It splits 

 easily into plates, which differ from the gypseous 

 in being flexible and elastic. These plates, when 

 of the purest kind, are transparent like glass, 

 but many are tinged with a variety of colours, 

 and are more or less opaque. Sometimes they 

 have a lustre resembling that of metallic sub- 

 stances, See. Sometimes talcs are in the form of 

 shining powder, like that which is used in bronz- 

 ing figures. The appearance has often imposed 

 upon miners, who have thought they met with 

 gold and silver, whereas there is never any metal 

 in these substances but iron. 



They are found also with other stones, as the 

 granite, which frequently contains a great quan- 

 tity of mica. Free-stone also contains more or 

 less. Its horizontal layers have between them a 

 thin stratum of talc, which makes the stone more 

 easily separable. Talc is also found in some kinds 

 of slate, which, when long exposed to the air, 

 moulder into talcky powder. The common talc 

 is used in making lanterns used in the powder- 

 rooms of ships, as they do not take fire or crack 

 with heat. 



VOL. II. K 



