DESCRIPTION OF THE DICHROlt. *>35 



also in some of the fragments of foliaceous granite, which 

 it includes. These fragments have evidently been exposed 

 to the action of heat ; and the primitive stratum, from 

 which they have been detached, is very proljably the 

 original matrix of the dichroit. In fact they exhibit in their 

 composition scales of black mica, and trapezoicial red gar- 

 nets similar to those we see contained in the masses, and 

 even in the interior of the crystals of this mineral, which 

 indicates a contemporaneous formation. The petrosiliceoua 

 lava, that commonly serves as a gangue, is rather granular 

 than compact. It is of the same nature as that of the 

 Ponce Islands, or that of the Puy-de-D6me, and of the 

 cascade of Mont-d'Or in France, being composed of very 

 fine grains of feldspar. The fire has left some very evident 

 traces of its action on the crystals and masses of dichroit: 

 most of the masses appear as if corroded in different places, 

 both internally and externally, and in the cavities are seen 

 portions of white scoriae, either intact or decomposed. The 

 crystals are almost all partly fused, cracked, and full of 

 flaws. Their fragments frequently present surfaces render- 

 ed dull by an extremely thin whitish coating, that conceals 

 the lustre of the fracture. 



From what has been said it appears, that the mineral of Reasons for 



Cape de Gattes diff'ers from all other known substances. "^'^'^'"^ '^ * 

 .... , . n^w species. 



Its primitive form, specific gravity, property of transmitting 



lays of two different colours, and the other positive or nega- 

 tive characters, that distinguish it more particularly from 

 " each of the substances, with which it is most likely to be 

 compared, are so discriminative, that we cannot avoid 

 considering it decidedly as a new species, without recurring 

 to the testimony of chemical analysis. At the same time it 

 seems to me most suitable to give it a name from its re- and gWing if 



markable property of double colour, and such is the etv- the name of 



^ ' •' . '' dichroil. 



mology of the name, which Mr. Ilaiiy had the goodness to 



suggest to me. I conceive myself sufficiently authorized 



to reject the denomination of yolite (violet stone), derived 



from the superficial colour of the crystals, because in the 



'present case its application would be more inconsistent than 



in many others. Besides, it is too liable to be confounded 



with hyalite, appropriated to the concrete hyaline quartz, 



or 



