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F. Slate breaks invariably into laminas or plates 5 

 opaque, not flexible ; in general does not ftrike 

 fire with fteel, though fome of the red flates 

 do; when written upon, the characters moftly 

 white ; effects with acids and with fire, various. 



There are many kinds of flate, as the black, 

 green, purple, blue, red, brown, grey, male bafs 

 or fhiver, plate flate, Irifh flate, &c. 



G. Fluor, is of a fparry or cryflalline appear- 

 ance, does not ftrike fire with fteel, or effer- 

 vefce with acids, vitrefcent per fe ; the moft re- 

 fractory is eafily fufible with borax or calcare- 

 ous earths ; being gradually heated it fhines 

 like phofphorus, but its light vanifhes before 

 it becomes red hot; as the cryftallized fluor, 

 irregular fluor, cubic fluor, and zeolites. 



H. Shirl, cockle or bafaltes, is a heavy hard 

 ftone fhoots into cryftals of a prifmatical figure, 

 moftly of a black or green color. 



3. Quartz, ftrikes fire with fteel, but does not 

 effervefce with acids, nor fall to powder after 

 burning. When pure cannot be melted per fe 9 

 but with alkaline falts moft readily into glals ; 

 texture folid, uniform ; particles homogeneous, 

 invifible, impalpable, as, 



a. Pure quartz, rock cryftal, or quartz cryftal, 

 fmoaky topaz, amethift, &c. 



b. Cryftals are diaphanous, hexagonal, colum- 

 nar, pyramidal; fome colorlefs, others milky, 

 yellow, brown, red, purple or black ; as cor- 

 nifh diamonds, Briftol ftones, &c. 



c. Flints, are femipellucid and detached ; break 

 in convex and concave polifhed fragments, as 

 the common flint, opal, onyx, Scotch pebble, 

 carnelian, mocha-ftone, chalcedony or white 



agate, 



