to8 Elements of Mineralogy. 



whereas that of quartz is (hattery ; it breaks 

 with fmooth furfaces, one of which is con- 

 vex, the other concave ; it is never found 

 cryftalized, but rather in feparate irregular 

 nodules, fcattered through other flrata, and 

 plentifully in England in beds of chalk; it 

 has feldoin any fiffures, with which quartz 

 abounds ; its fpecific gravity is from 2,65 to 

 2,700. 



Flints are infufible per fe in the ftrongeft 

 fire, but generally become white and brittle 

 by reiterated calcination, which feems to in- 

 dicate that they all contain a little water ; and 

 hence alfo, their decrepitation, when heated ; 

 The fame may be faid of quartz ; they are 

 affe&ed by fluxes in the fame manner as the 

 pureft ftones of this genus. 



The common brown flint exhibited on Mr. 

 Wiegleb*s analyfis 80 per cent, of filiceous 

 Earth, 18 of argill, and 2 of calcareous. 6 

 N. Aft. Natur. Curiof. p. 408. Coloured 

 flints undoubtedly contain metallic particles. 



To this fpecies we muft alfo annex the 

 finer flints commonly called Egyptian pebbles^ 

 hsemachates, ftigmites, filex fardus. Thefe 

 differ from common flints; i ft * in this, that 

 they are lefs, if at all tranfparent ; 2 d . that 

 their texture is finer, harder, and clofer, and 



theif 



