BUTE. MINERALS. 473 



mens. Occasionally, it is crystallized at liberty within the 

 cavity ; the hexagonal plates being accumulated into hemi- 

 spherical bodies so as to present the appearance known to 

 mineralogists by the name of coxcomb, and common in 

 sulphat of barytes. In other cases it seems to be peculiarly 

 associated with the veins and nodules of quartz that are 

 found in the schists. When that happens, it is sometimes 

 disposed in lamina? among the quartz, at others in irregular 

 nodules. In this situation it is also sometimes crystallized, 

 and either totally or partially imbedded in the quartz. 

 These crystals consist of a prolonged hexagonal prism, 

 generally incurvated in various directions, and often much 

 contorted into vermicular forms. The edge of each scale 

 is visible on the surface of the prism, so that the whole 

 presents a transversely striated aspect. Such crystals are 

 well known to collectors as being sometimes entirely im- 

 bedded in transparent quartz ; in which case they are much 

 valued. Where the quartz and chlorite are thus associated, 

 the former is frequently found of an intense dark green 

 colour, but still possessing its natural lustre ; and, although 

 opake in the mass, translucent on the edges. Although 

 the colour is in this case evidently the result of the 

 chlorite, since the scales of this substance are often found 

 distinctly visible and producing a more dilute tint of green, 

 it is impossible, in the darkest specimens, to distinguish 

 it from the quartz, the mineral presenting a uniform and 

 simple texture. As happens in the case of prase, which 

 bears the same relation to actinolite, the colouring matter 

 appears as if it existed in the quartz independently of the 

 substance to which it might be supposed attached. This 

 green quartz is sometimes crystallized, but the forms, as 

 far as I observed any, are incomplete ; although such 

 faces as actually occur, possess the same incidence on each 

 other as those of a simple quartz crystal ; affording a proof, 

 like the spar of Fontainebleau and other analogous cases, 

 that the form of a crystal is not necessarily affected by the 

 mixture of another substance. The mineral thus described 



