Elements of mineralogy, crystallography and blowpipe analysis from a practical standpoint .. . per occurring in groups like Fig. 313, com-posed of cubes each twinned parallel to anoctahedral face and these twins united in par-allel position so as to form branches at sixtydegrees to each other as shown in ideal * Am. Journ. Sci., XXXII., p. 428, 1886. 140 DESCRIPTIVE MINERALOGY. Surface Irregularities. Etchings.—The perfectly smooth and plane surface is difficult tofind, frequently the surfaces are more or less corroded by naturalagencies, and many show natural etch figures simi
Elements of mineralogy, crystallography and blowpipe analysis from a practical standpoint .. . per occurring in groups like Fig. 313, com-posed of cubes each twinned parallel to anoctahedral face and these twins united in par-allel position so as to form branches at sixtydegrees to each other as shown in ideal * Am. Journ. Sci., XXXII., p. 428, 1886. 140 DESCRIPTIVE MINERALOGY. Surface Irregularities. Etchings.—The perfectly smooth and plane surface is difficult tofind, frequently the surfaces are more or less corroded by naturalagencies, and many show natural etch figures similar to the arti-ficial etch figures described on p. 148. Striations.—Sometimes crystal faces are marked by fine paral-lel straight lines which are really fine grooves each boundedby two definite ciystal planes. They may result either from acontest between two crystal forms as in the case of the striations Fig. 314. Fig. 315.
Size: 1199px × 2084px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, bookpublishernewyorkdvannostran
