436 Prof. Maskelyne and Dr. Lang's Mincralogical Notes. 



They are the result of an accidental crystallization occurring after 

 the expulsion of the mercury from a mass of the gold amalgam 

 obtained in the ordinary way. 



The crystals, which are tolerably large, had a pyramidal ap- 

 pearance from the want at certain planes of the cube and the 

 dodecahedron, as is shown in Plate VII. figs. 1 and 2. Only the 

 planes which are represented in the figures were well developed ; 

 no planes could be observed on the posterior side. Several small 

 planes were found to belong to the two forms (1 I 3) and (1 2 3), 

 the latter of which has, I believe, not yet been observed on cry- 

 stals of gold. The data for the calculation of the indices of this 

 form were (fig. 2), — 



Obs. Calc. 



012.321= 60° 30 61 27 



1 2 . 3 1 I = 97 97 46 



L.012.101 = 129 129 15 



021 .321 = 52 50 53 18 



9. On some Combinations of Eudialyte. By Viktor von Lang. 



There are in the handbooks of mineralogy only two or three 

 combinations of eudialyte represented by drawings. I have under- 

 taken therefore to add a few more, the forms of which were ob- 

 served on crystals from Kangersluardsuk, South Greenland, in the 

 mineral collection at the British Museum. In studying these 

 crystals also three new planes were found, so that the planes now 

 known on this mineral are 



o(lll), a (Oil), b (2 II), r(10 0), t (2 1 1), y (6 1 1), 



c(011) 3 s(Ill), A (12 2), *(201), n(210), 



y, h } n being the new planes. Pig. 7, PL VII. gives the principal 

 zones formed by these planes. 



Prof. Miller* found for this mineral, from very careful mea- 

 surements, the crystallographic element 



ro = 67° 42', 



by the aid of which the following calculated angles are deduced. 

 The observed combinations and the measurements made to 

 determine the position of the new planes are : — 



Fig. 3.— o (1 1 1), a (0 1 I), r (1 0), e (0 1 1). 



Fig. 4.— o (1 1 1), a (0 1 I), b (2 1 1), r (1 0), y (6 1 1), 



*(211), e(011), s(Ill), 



yo = 56° 44' calc, 56° 48' obs. 



* Phil. Mag. vol. xvi. (1840) p. 477. 



