144 CONTRIBUTIONS TO MINERALOGY. [bull. 262 
measured as separate crystals may, in reality, be parts of one and th< 
same crystal. 
As may be expected, the crystals of lepidolite are similar to-thosi 
of muscovite. They also show, however, some marked differences 
The interfacial angles are nearly the same and the crystals are natur 
ally referred to the same axes as muscovite. There are three market 
differences between these crystals and those of muscovite: (1) Tin 
rarity of twins, only one being found in twenty-one crystals; (2) th< 
absence of the characteristic face of muscovite, M = {221}; and (3) th< 
presence of the a face {100}, occurring on 10 out of 21 crystals. Th<; 
crystals are not so striated as the green North Carolina muscovites 
for instance, and in many cases the faces yielded perfect signals. 
The common forms are c = {001}, 5 = {010}, a = {100}, e = {023} 
o = {112}, M = {ill}, and x — {131}. Besides these the following hav( 
been determined: N— {261}, z ={132}, £ = {130}, and possibly several 
others, as {223}, {221}, {112} ; also a number of forms which occur fon 
the most part as broad faces, giving good reflections, but having 
anomalous indices, and which need further study. 
The most frequent combination is c b o u ,/', after which comes c h h 
u x e a. Whenever the angle (001): (010) could be accurately measures 
it was found to be exactly 90° 00' in every case, and the distribution 
of the faces also indicates monoclinic symmetry. 
It was noticed that the angle between the same forms varied slightlj 
on different crystals. The faces were smooth and highly polished, anc 
the angles could easily be measured with an error not greater than V 
It is suggested that this variation is real, and is due to the fact thai 
lepidolite is an isomorphous mixture of two end products, and as the 
ratio of these two products varies, the crystallographic and physics 
properties of the mineral also vary. Further study on the possibj 
correlation of the various properties of the mineral is under way. 
This lepidolite belongs to the "second class" of Tschermak or the 
u brachy diagonal class" of Scharizer — i. e., the axial plane is paralle 
to the clinopinacoid and not normal to it. The trace of the axial plant 
was always parallel to one arm of the percussion figure. 
The above is only a brief preliminary statement. The detailed crys- 
tallography of the mineral will soon be published in a paper on the* 
mineralogy of this entire held of lithium minerals in southern California. 
The writer's thanks are due Mr. Dan Mcintosh, jr., of Ramona, the 
owner of the mine. 
