152 Elements of Mineralogy. 



filiceous ground ( generally jafper, chert, 

 fhoerl, or lava) contain either feltfpar, quartz, 

 fhoerl, mica, ferpentine, or other fpecies of 

 flone in a cry ft aline form. When its ground 

 is jafper it is hard. It is commonly either 

 red, purple, grey, green, or black, according 

 to the ground. The red commonly contains 

 feltfpar in fmall white dots or fpecks, and 

 often together with thefe black fpots of fhoerl. 

 The green is either a jafper or fhoerl, with 

 fpots pf quartz or fhoerl. Sometimes a por- 

 phyry of one colour contains a fragment of a 

 porphyry of another colour; the green are often 

 magnetic. Thofe that have chert for their 

 ground, are fufible per fe. 



SPECIES VI. 

 Compounds of the Siliceous, and various Genera, 



I. VARIETY. 

 * 



1. >uartz 9 Mica, ^nd Serpentine, 



2, Quartz, Mica, and Steatites, 



3. ^yartz^ Mica, andShoerl> together 'with 

 Serpentine or Steatites, or Soap-rock. 



4. Quartz, Felt-fpar, Mica> and Serpen-* 



All 



