26 



This form has probably not been observed before on cal- 

 cite. The corresponding positive scalenohedron , on the other 

 hand, has been observed on crystals from Traversella, Alston 

 Moor, and Ahrenthal M- The negative rhombohedron (/9) is like- 

 wise now observed for the first time. It is determined by its 

 position in the zones [3582, TlOl] and [lOFl, 385^2]. 



The crystals belonging to this type are almost colourless 

 and tolerably clear. They were found at the locality No. 2, but 

 only in small numbers. On the same specimens there also 

 occur small crystals of analcime, which are evidently of earlier 

 formation than the calcite. 



Calcite crystals of the fourth type have been observed only 

 on a single specimen , which was found loose in the neigh- 

 bourhood of the locality No. 5. These crystals (Fig. 8, Plate 1) 

 show exclusively the forms 



с = {0001} and /-={0221}. 



As the forms are nearly equally developed, a crystal habit 

 rather uncommon on calcite arises, the crystals assuming a 

 certain resemblance to regular octahedra. The crystals were, 

 indeed, at first regarded as belonging to the cubic system and 

 supposed to be an unknown mineral. On a closer examination 

 of the presumed new mineral, it, however, soon proved to be 

 nothing but calcite. The crystals are only a millimetre or two 

 in diameter. The planes are tolerably even, but not very 

 bright, and have a brownish tarnish. 



In digging at the locality No. 2, the medium-grained syenite, 

 was found to be split by crevices of comparatively recent 

 date. The walls of these crevices were lined with thin crusts 

 of snow-Avhite calcite, resembling on efflorescence. On these 

 crusts no distinct crystal forms are observable. The surfaces 

 are papillose and have a stalactitic appearance. 



') J. R. McD. Iiby, Ref. Zeitschr. f. Kryst. Vol. 3 p. G17. 



