584 ULVA, &C. MINERALS. 



an analogous nature occurring in the case of other crys- 

 tallized compounds. The difficulties which such facts 

 present to a system of mineralogical distinctions founded 

 on geometrical characters, are too well known to be here 

 enforced ; as the fragment of analcime cannot be distin- 

 guished in some cases from that of quartz, even when 

 the form of the crystal is perfect. 



It is among these transitions that a botryoidal sub- 

 stance is found, which, when of a flesh colour, has been 

 called sarcolite. This mineral is not however necessarily of 

 that colour, being sometimes white, while it is occasionally 

 also of a strong red. In the latter case it can sometimes 

 scarcely be distinguished from chert but by its transition 

 and connexions; the red colouring matter abounding so 

 as to destroy the lustre and transparency. This variety 

 also occasionally passes into pure quartz, still maintaining 

 the red colour. I may add to these varieties of analcime, 

 that in the same situations, it is occasionally found crystal- 

 lized, and of a bright and strong red colour. 



