1883.] Mr Solly, Crystallographic Notes. 407 



(4) Crystallographic notes. By R. H. Solly. 



Euchroite Cu 3 As 2 8 + H 2 Cu0 2 + 6aq. 



When registering the specimens of Euchroite in the University 

 collection I noticed that some of the crystals exhibited the faces 

 (Oil) (012) with the common combination. 



As I am unable to find these faces recorded in any work, I 

 therefore give the following angles I obtained with their calculated 

 values : 



Found Calculated 



(Oil) (001) 59.26 59.36 



(Oil) (110) 42.30 42.331 



(011) (101) 69.22 69.26 



(012) (001) 39 .40 40 . 26 



The faces (001) and (110) were uneven and striated. The 

 face (012) narrow and dull. 



Hoping to find better crystals I examined the specimens at 

 the British Museum and the Royal School of Mines, the latter 

 place now contains the very valuable Ludlam Collection, but I 

 was disappointed as neither collections possess crystals exhibiting 

 this combination. 



The figure in Plate X. represents these new forms drawn in 

 fair proportion to the other faces. 



Orthoclase. 



When demonstrating last term on Orthoclase and making 

 projections and drawings of some of the principal crystals for the 

 use of the students, I noticed on an Elba specimen a well de- 

 veloped rough face (10 8 1) in the zone [110 201]. The roughness 

 of the plane made it impossible to read with any degree of 

 accuracy. So I endeavoured by searching through other col- 

 lections to find a crystal with this face evenly developed. 



The Royal School of Mines does not possess one. Prof. 

 Warrington Smyth's valuable collection, which is very rich in 

 Elba specimens, does not contain one exhibiting this face, and this 

 was also the case in other private collections which I had the 

 opportunity of examining. 



In the British Museum I could only find one crystal exhibiting 

 this face, which was kindly placed for me on one of Fuess's 

 goniometers ; though the plane was well developed (on account of 

 the same roughness) it gave no better results than the specimen 

 in the University collection. 



Found Calculated 



(110) (10 81) 6°. 30'— 7°. 30' 7°. 2' 



