94 J a jf sr > Labrador Stone, &c. [Book VL 



very hard, and admit a good polifh ; and they are 

 variegated with different colours' They are feldom 

 ranged in flrata, but form confiderable maffes and 

 veins in rocks. They are alfo found in fmall round 

 maffes. The principal fpecies of jafpers are the fol- 

 lowing the white, grey, yellow, red, brown, green, 

 veined, fpotted, flowered, and green with red points, 

 or blood-ftone. Toys, and more efpecially cups and 

 faucers, are made of jafper. Many antique fculp- 

 Cures are on flones of this nature. 



V. The mod common kind of FELDT-SPAR is 

 formed of rhombic laminae, and has therefore obtained 

 the name of rhombic quartz. It gives fire with flee), 

 whence it has been called fpathum fcintillans. It is 

 harder than the fchifti, and is fufible. It is found in 

 locfe malTes, two inches long, or mixed with fand, 

 clay, &c. or bedded in granite. It is ufed in making 

 china at Drefden. Its colours are white, red, brown, 

 pale, yellow, or greenifh. 



The Labrador-ftone is generally claffed with the 

 feldt-fpars. It admits of a very fine polifh, and when 

 in that ftate reflects a variety of beautiful colours. The 

 (lone itfelf is of different fhades of grey. 



VI. SHIRL or COCKLE, of different fhades of green j 

 and the various fpecies of whetftones, are alfo com- 

 monly referred to the filiceous order, though th~ Iattef ; 

 are generally in fome meafure compound. 



The ufes of the flinty fubftances are various, and 

 have been partly intimated; but there is one art, in 

 which their ufe is too confpicuous to be pafled over in 

 filence. 



The art of making glafs depends, on the fufion of 



fearthy 



