Proceedings of the United States National Museum . the symmetryof that system have apparently never been e assignment of the mineral to the monoclinic sys-tem of crystalhzation depends upon the optical struc-ture of crystals which, when lying on the h (010) face,show optical anomalies with two twinning planesintersecting each other at right angles and divid-ing the crystal into 4 identical quarters. Goldschmidt has disregarded the optical structure and classesstilbite ( = desmin, Germ.) as orthorhombic. Epidesmine has been described as an orthorhombic mineral havingcrystals bounded by
Proceedings of the United States National Museum . the symmetryof that system have apparently never been e assignment of the mineral to the monoclinic sys-tem of crystalhzation depends upon the optical struc-ture of crystals which, when lying on the h (010) face,show optical anomalies with two twinning planesintersecting each other at right angles and divid-ing the crystal into 4 identical quarters. Goldschmidt has disregarded the optical structure and classesstilbite ( = desmin, Germ.) as orthorhombic. Epidesmine has been described as an orthorhombic mineral havingcrystals bounded by three pinacoids at right angles to each the formula given for epidesmine is slightly different than thathere adopted for stilbite, the analysis, quoted above, is well withinthe limits of variation of stilbite analyses. The only distinctionbetween stilbite and epidesmine would then appear to be that thecrystals of the latter are presumably homogeneous with parallel ex-tinction on (010) while the crystals of stilbite are twinned vnih a. Fig. 25.—Stilbite ofthe usual habitshowing pyrami-dal faces. 74 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL. 6G.
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Keywords: ., bookauthorun, bookcentury1800, bookdecade1870, booksubjectscience
