163 Notice of Minerals fi^om New Holland. 



I think, that they cannot be regarded as pseudomorphs of any 

 other mineral, from the agreement in the value of their angles as 

 measured by the goniometer, compared with those of the obtuse 

 rhomboid established as the fundarnental form of the species, as 

 well as from the fact that the crystals are imbedded in cacholong, 

 which now occupies the interior of the geodes. If pseudomor- 

 phous, the mineral of which they are imitative must have been 

 removed so as to admit of a subsequent infiltration of the cacho- 

 long. It is more probable that the quartz and cacholong were 

 formed at the same time, the latter affording a soft matrix in which 

 the crystalhne molecules could freely arrange themselves, accord- 

 ing to the laws which governed them. 



Two other modifications of rhombohedral quartz were met 

 with among these specimens, of comparatively rare occurrence. 

 In one, the primary rhomboid, by a very deep truncation of its 

 lateral solid angles, has given rise to long six-sided prisms, termi- 

 nated by trihedral summits, there being no triangular replace- 

 ments upon the upper edges of the rhomboid by 

 which the usual six-sided pyramids are produced. 

 See Fig. 7. On some of the rhomboids, however, 

 which do not present any portion of the faces par- 

 allel with their axes, we may observe the small 

 triangular planes which finally- produce the six-sided 

 pyramids. The terminal primary planes P, are 

 smooth and bright, while the elongated faces r, 

 are curved and roughened by transverse strias. Sometimes the 

 usual six-sided prisms, terminated by similar pyramids, have their 

 alternate lateral solid angles replaced by small rhombic planes 

 inclining equally upon the sides of the prism, producing the quartz 

 rhombifere of Haiiy. The sides are also striated parallel with 

 their edges of combination with the faces of the pyramids. This 

 author, (Traite de Mineralogie, tome second, p. 413,) describes 

 these rhombs as existing onli/ on the alternate angles, but in the 

 later works of Mobs, Beudant and others, they are figured also 

 upon the intermediate angles, being always represented as cover- 

 ing but a very small portion of the acuminating pyramids. Ac- 

 cording to PhiUips, the " Bornholm diamonds" afford the most 

 perfect examples of this modification. 



Green Chalcedony and Heliotrope. — This first mentioned min- 

 eral is of a deep serpentine green color. It breaks with a con- 



