162 Notice of Minerals from 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 fundamental 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 psendomor- 
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 crystalline 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. 
Tn 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, 
Fig. 7. 
are curved and roughened by transverse striz. 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 
rhombifére of Haiiy. The sides are also striated parallel with 
their edges of combination with the faces of the pyramids. "This 
author, (‘Traité de Minéralogie, tome second, p- 413,) describes 
these rhombs as existing on/y on the alternate angles, but in the 
later works of Mohs, 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- 
eording to Phillips, the “Bornholm diamonds” afford the most 
perfect examples of this modification. 
aes reer Chalcedony and Heliotrope.—This first mentioned min- 
ral is of a deep serpentine green color. It breaks with a con- 
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