MODE VI. PORPHYRIN. 8J 



Aspect 4. Green. Resembling the red. 



The same, with crystals of s'iderite. 



From Ferber's description it would seem that 

 the felspar is wanting, in which case it is a trap 

 or basal tin. 



The same, with small crystals of felspar in 

 white spots, commonly irregular, and twisted like 

 worms; the Porfido verdejiorito*. 



The red also occurs in Egyptian monuments, as 

 well as the black f. Green porphyry is also found 

 in Corsica and Norway. 



MODE VI. PORPHYRIN. 



This name has been adopted for porphy- 

 ritic substances, in which the crystals of fel- 

 spar are so small as almost to escape the eye, 

 or not be discoverable without a lens. But 

 somewhat of the regularity of true porphyry 

 must be observable, otherwise the substance 

 must be considered merely as a mingled basaltin. 

 On the other hand, the mixture of a few grains 

 of quartz may be admitted in a porphyrin ; but 



* One kind so called is not a porphyry, but a waved mixture of 

 siderite and felspar, as if daubed with a brush. See Anomalous 

 Rocks. 



t Wad, 12, 13. 



