226 W. T. Schaller — Crystallography of Lepidolite. 



= {130}, and possibly several others, as {223}, {221}, {112}. 

 Also a number of forms occurring for the most part as broad 

 faces, giving good reflections but having anomalous indices and 

 which need further study. The most frequent combination is 

 cboux, after which comes cbouxea. Whenever the angle (001) : 

 (010) could be accurately measured, it was found to be exactly 

 90° 00' in every case, and the distribution of the faces also indi- 

 cate monoclinic symmetry. 



It was noticed that the angle between the same forms varied 

 slightly on different crystals. The faces were smooth and 

 highly polished and the angles could easily be measured with 

 an error nor greater than 1/. It is suggested that this varia- 

 tion is real and is due to the fact that lepidolite is an isomor- 

 phous mixture of two end products, and as the ratio of these 

 two products varies, the crystallographic and physical proper- 

 ties of the mineral also vary. Further study on the possible 

 correlation of the various properties of the mineral is under 

 way. 



This lepidolite belongs to the " second class " of Tschermak 

 or the " brachydiagonal class' 1 of Scharizer, i.e., the axial 

 plane is parallel to the clinopinacoid, and not normal to it. The 

 trace of the axial plane was always parallel to one arm of the 

 percussion figure. The above is only a brief preliminary state- 

 ment ; the detailed crystallography of the mineral will soon be 

 published in a paper on the mineralogy of this entire field of 

 lithium minerals in southern California. The writer's thanks 

 are due Mr. Pan Mcintosh, Jr., of Ramona, the owner of the 

 mine. 



Chemical Laboratory, U. S. Geological Survey. 



