Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/92

 As far as I have observed, the chabasite which I have described is never, like the analcime, imbedded in the filamentous mesotype, but is not unfrequently associated in the same cavity both with stilbite and with analcime, nor is it unusual to find minute and well formed crystals of this latter substance, imbedded in the crystal of chabasite. In some cases perfect crystals of chabasite are lightly sprinkled over the surface of crystals of stilbite, adhering so slightly as to fall off on the slightest concussion: in other cases crystals of this mineral, as well as of the analcime, are confusedly mixed with rhomboids of carbonate of lime, hereafter to be described.

The primitive crystal of this mineral is by much the most common, its modifications being rare and offering but few varieties; it is very frequently twinned, the angles of the one crystal appearing on the faces of the other, nor is it uncommon to meet with it in triplets, or even in more complicated groups, displaying an irregular mixture of prominent angles. The most common modification consists in the truncation of one angle; sometimes two neighbouring angles are truncated, and occasionally this defect extends to three, the truncations being often so deep as to remove a third part of the rhomb. In other modifications a single angle and a single edge are removed, or the truncations extend to two angles and two edges; but I have not observed any specimens in which these defects were extended to a greater number of edges. The edge is in some cases replaced by two or by three planes, or even by a greater number, so as to appear nearly rounded; and each face of the rhomb is also frequently replaced by two planes meeting in an edge diagonally extended and sometimes rising by successive stages of planes parallel to the. original face.

These crystals are sometimes opaque, more frequently transparent, but in by far the greater number of instances they acquire a