Mineralogy of Sky. 83 



type hereafter to be described, and the crystals thus seem to be im- 

 bedded in a mass of cotton. 



The size of the crystals varies from that of a pin's head to the 

 diameter of half an inch ; but in general they present only one mo- 

 dification, the twenty-four sided crystal with trapezoidal faces, of 

 greater or less regularity. The only other form which I found was 

 the primitive, and of that 1 procured but two specimens, while a 

 ship might be loaded with the trapezoidal variety. The crystals de- 

 scribed are sometimes opake and white, at others they are mottled 

 with a mixture of opake and transparent parts, while in a third, 

 but less common case, they are transparent. In this latter case, 

 when minute, thev sometimes transmit the black colour of the sub- 

 jacent basalt to which they adhere, so perfectly as to resemble a 

 velvety surface of black crystals. In similar circumstances, trans- 

 mitting the greyish or ochry colour of the substance to which they 

 are attached, they appear to possess a colour which a more narrow 

 inspection shows to be fallacious. A few specimens however occur 

 of a flesh red, a colour frequently found in almost all the minerals 

 of this family, and very predominant in the different zeolites which 

 occur at Glen Farg in Perthshire. I also found a solitary specimen 

 of a pale sea green colour, but did not observe that variety of a 

 pale bluish grey, which, in company with the flesh coloured and 

 yellow green, I have seen in the rocks at Larne in Ireland. 



Chabasite is found in similar circumstances on the same shore, 

 but it is comparatively of very rare occurrence : it abounds however 

 in the rocks at the Storr, which for a considerable space consist of 

 an amygdaloid containing it accompanied by stilbite. It is here so 

 common, occupying cavities of greater or less magnitude, that a 

 fourth or fifth part of the total bulk of the rock is sometimes con- 

 stituted by the chabasite. 



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