69 



All the pieces are from one single pegmatite vein of the 

 transformed foyaite. The vein is still more transformed than 

 the rock itself, so that nothing of the original structure can be 

 traced. The presence of an original pegmatite vein may be 

 inferred from the fact that the cavities with ilvaite are much 

 larger than in the surrounding parts, and may reach to sizes 

 of several dms. Otherwise the rock consists of alternating 

 parties of grained albite and ilvaite, on which crystals of both 

 minerals are sitting, among which crystals of the latter mineral 

 are by far Ihe most predominant. The most characteristic 

 feature of the occurrence is that in all the cavities are found 

 numerous octahedral crystals of a bright, bluish green fluorite, 

 and then all the intervals are fdled with snowy white calcite, 

 one individual in each cavity. The different strong colours: 

 black ilvaite, white calcite, and bluish green fluorite make a 

 very beautiful mixture. When the calcite is decomposed in 

 hydrochloric acid, we get a splendid mixture of crystals of 

 fluorite and ilvaite ; where the calcite is found decomposed in 

 nature, the latter crystals are as usual very dull, partly with 

 natural etching figures, which are to be more particularly men- 

 tioned hereafter. Besides the minerals mentioned, rather poorly 

 developed crystals of sphalerite may sometimes be found. 



The form of the crystals of ilvaite is not much different 

 from that of type XII, from which type the present one is 

 chiefly only distinguished on account of the different way of 

 occurrence. The great majority of crystals are very simply 

 constructed, as shown in the first of the figures below; to this 

 may then in a few of the crystals be added more or fewer of 

 the before mentioned faces; the most complete combination is 

 represented in the second figure; every possible transition be- 

 tween these two forms is found. 



Combination in the crystals least rich in faces: b{010}, 

 s{l20}, /г {210}, w{ZOl}, F{\Ol}, f{Oil}, in the crystals most 



