fotne Mineral Subjlances. 29 
Mica or Glimmer. This is lighter than any of the 
fparry fubftances ; is compofed of very thin flexible 
flakes, more or lefs large. Many of this kind are found 
in form of fmall coloured fcales of various colours, and 
very much refemble the bronzes. 
Tin fpar, or white tin ore, fee its defcription here- 
tofore. 
White lead ore is found of a great variety of forms ; 
is very heavy, effervefces with the acids of nitre and fea 
fait, and totally diffolves in them, with the help of heat. 
With the acid of fait it forms cryftals much refembling a 
lilver coloured glimmer, juft as common lead would have 
done, and with the acid of nitre it forms regular cryftals. 
The fpathofe iron ores, when powdered and put on a 
red-hot iron or ftone, inftantly become black, and look 
like a black, fhining, micaceous iron ore. 
Zeolite is lighter than the calcareous fpars : fee its pro- 
perties already defcribed. 
Of a Jet of fpars wbofe properties were not hitherto known, 
and experiments made on one of them. . 
This fpar cryftallizes in form of flat, and alfo of folid, 
rhomboidal cryftals, and is found of a great variety of 
colours, fuch as white and femi-tranfparent, of a pearl 
colour. 
