W. T. Schaller — Crystallography of Lepidolite. 225 



Art. XYII. — Crystallography of Lepidolite ; by Waldemar 



T. Schaller. 



A group of lepidolite crystals was collected by the writer in 

 the summer of 1901, at a gem mine about four miles east of 

 Ramona, on the stage road from Ramona to Julian, San Diego 

 County, California. The mine was opened and worked for its 

 gems, such as topaz, tourmaline, garnet, etc. With these are asso- 

 ciated quartz, orthoclase in good crystals at times several feet 

 long, and muscovite, and, rarely, lepidolite. The minerals in 

 question all occur in the loose dirt, filling " pockets" in a 

 pegmatite dike. 



The specimen of lepidolite under consideration consists of a 

 group of intergrown crystals which often reach a large size. 

 The group itself is about 5 cm thick and the individual crystals 

 measure about l cm across the base, though ones with a diameter 

 of 2 cm are not rare. The crystals are also proportionally thick, 

 the average being from 2 to 4 mm , though a few are somewhat 

 thicker. They are transparent and of a very pale # pink color, 

 and, in the direction normal to the vertical axis and parallel to 

 the base, of a slightly deeper tint. They fuse easily to a white 

 enamel, coloring the flame an intense crimson. The side faces 

 are usually plain, not rounded nor striated, and of a brilliant 

 polish, giving excellent signals. It is, however, extremely 

 difficult to secure a complete crystal from the group, owing to 

 the perfect basal cleavage which will cause a crystal to split 

 into a number of layers. This will also at times cause part of 

 a crystal to become slightly displaced. In consequence of this 

 difficulty, most of the crystals measured are only parts of the 

 original crystals, and two such pieces measured as separate 

 crystals may, in reality, be parts of one and the same crystal. 



As may be expected, the crystals of lepidolite are similar to 

 those of muscovite. The interfacial angles are nearly the 

 same and the crystals are naturally referred to the same axes 

 as muscovite. There are three marked differences between 

 these crystals and those of muscovite : (1) the rarity of twins — 

 only one being found in twenty-one crystals ; (2) the absence 

 of the characteristic face of muscovite, M = { 221 } ; and (3) the 

 presence of the a face { 100 } , occurring on ten out of twenty-one 

 crystals. The crystals are not so striated as the green JNorth 

 Carolina muscovites for instance, and in many cases the faces 

 yielded perfect signals. 



The common forms are_c = {001 J, h = {010}, a = {100}, e 

 = {023}, o= {112}, w = {III}, and a; = {131}. Besides these, 

 the following nave been determined ; 2T= {261}, z — {132}, 1 



