[ 432 



LX. Miner alogical Notes. By Professor Maskelyne and 

 Dr. A^iktor von Lang, of the British Museum. 



[Continued from p. 58.] 



[With Four Plates]. 



7. On the Crystalline Form and the Optical Properties of Malachite, 

 By Viktor von Lang. 



MALACHITE crystallizes in the oblique system ; but hitherto 

 the whole of its completely crystallographic elements were 

 not capable of being determined, as on the crystals of this mineral 

 there had only been found the planes 110, 10 0, 010, 101, 

 which do not yield a sufficient number of independent angular ele- 

 ments for the purpose. But there are in the mineral collection of 

 the British Museum crystallized specimens from several localities, 

 on which several other planes besides these occur. The angles 

 of these new planes could not be determined with great accuracy, 

 partly because the crystals themselves are very small, partly also 

 on account of the imperfection of these faces. But as the final 

 results are in tolerably good accordance, and as some of the cry- 

 stals investigated differ in their form from those hitherto known, 

 I will give here the description of them, adding some remarks 

 on the optical properties of malachite. 



The following planes have been observed (Plate VI. fig. 10) : — 



100, 010, 110, 101, 102, 10 3, 104, 112, 124, 13 4; 

 and from the measurements the crystallographic elements 



«: b : c=0-8173 :1 : 04231 



ac =91° 30' 



were deduced. With them are calculated the angles of the fol- 

 lowing Table : — 





100. 



001. 



010. 



110. 



110. 



101 



o 1 



61 27 



27 3 



90 6 



o / 



68 17 



o / 



111 43 



102 



103 6 



18 36 



90 



100 7 



79 53 



103 



98 19 



9 49 



90 



96 26 



83 34 



104 



95 53 



7 23 



90 



94 33 



85 27 



112 



102 50 



.18 28 



78 21 



92 32 



72 34 



124 



95 45 



13 58 



78 7 



86 58 



78 1 



134 



95 37 



18 58 



72 29 



83 25 



74 34 



