32 



Referred to this system of axes, the 16 forms observed 

 by me that could be determined with any degree of certainty, 

 receive the following symbols: 



с = {0001}, ш = {10Го}, w = {n2b}, i = {lT05}, ^ = {2029}, 

 и = (2209), q = {ПО2}, r = {2023}, v = {3034}, у = {3304} , 

 29 = {l0Tl], s ={4043}, « = {3032}, /? = {3302}, ^ = {330l}, 

 z = {l\2l]. 



The crystals most frequently met with are, as already men- 

 tioned, small in size and of acute rhombohedral habit. The 

 predominant form is a, which, together with the base, is in 

 most cases alone present, fig. 2, Plate II. Besides these forms the 

 crystals often show the more acute negative rbombohedron y, 

 forming with the former parallel combination-edges (fig. 3, Plate II). 

 The more obtuse negative rbombohedron y is less common on 

 these crystals ; it occurs in combinations represented by fig. 4, 

 Plate II. This form, as well as the other more obtuse rhombo- 

 heda is present chiefly on the larger crystals. 



These larger crystals present, with regard to their deve- 

 lopment, a highly prominent peculiarity. While on most crystals 

 the more obtuse forms (those with the c-axis shorter) are found 

 at the ends and the more acute forms at the middle edges, 

 the reverse is the case with the larger crystals. They are ter- 

 minated at the upper and lower ends by the acute forms (those 

 with a long c-axis), and the more obtuse forms present a larger 

 or smaller protuberance at the middle, fig. 5, Plate II. These 

 balllike central parts of the crystals often differ as to their cha- 

 racter or condition from the rest of the mineral. While the 

 mineral in general is quite fresh, there portions seem to have 

 undergone some sort of alteration. The faces that occur have 

 only a waxy shimmer or are quite dull, so that perceptible 

 reflexions are seldom obtained from them. The determination 

 of the forms in these portions has, therefore, presented great 

 difficulties. The forms i, t, и and s have been determined 



