. Bulletin - United States National Museum. Science. 426 BULLETIN 131, UNITED STATES NATIONAL MUSEUM It gave qualitative reactions for copper and arsenic and was found by A. Rodolfo Martinez to have optical properties in agreement with those given in Larsen's tables for trichalcite as shown by the following comparison: Comparison of optical properties of trichalcite Pine Creek, Idaho (Martinez). Color pale bluish-green. Nonpleochroic. Biaxial. Sign negative (—). 2V large. 1=1. Birefringence medium low. X normal to plates. Turginsk, Urals (Larsen). Color pale bluish-green. Nonpleochroic. Biaxia
. Bulletin - United States National Museum. Science. 426 BULLETIN 131, UNITED STATES NATIONAL MUSEUM It gave qualitative reactions for copper and arsenic and was found by A. Rodolfo Martinez to have optical properties in agreement with those given in Larsen's tables for trichalcite as shown by the following comparison: Comparison of optical properties of trichalcite Pine Creek, Idaho (Martinez). Color pale bluish-green. Nonpleochroic. Biaxial. Sign negative (—). 2V large. 1=1. Birefringence medium low. X normal to plates. Turginsk, Urals (Larsen). Color pale bluish-green. Nonpleochroic. Biaxial. Sign negative ( —). 2V large. a=h 67 ± 0=1. 686±0. 003. 7 = 1. 698 ±0. 003. Birefringence X normal to Upon examination of the specimen under a binocular microscope it was found that the mineral was in thin tabular crystals of hexagonal aspect and although these were very minute it was found possible to measure two of them on the 2- circle goniometer. The basal pinacoid gave good signals but the very nar- row prismatic planes were more or less curved and irregular, yielding only approximate measure- ments accurate, perhaps, to 1°. These indicated 60° angles for the pris- matic zone, the mineral thus simulating hexagonal crystallographic symmetry. Examination of the measured crystals in polarized light shows them to be made up of biaxial orthorhombic sectors as shown in Figure 138. The sectors have interlocking boundaries and each sector has well-defined cleavage parallel to its edge. The end sectors give parallel extinction and in convergent light give a per- fectly centered biaxial interference figure. The lateral sectors have a confused structure as though made up of overlapping plates. It is evident that the several apparently prismatic planes of the pseudo- hexagonal tablet are pinacoids of several orthorhombic units which go to make up the twinned group. It is probable that trichalcite is orthorhombic, with a prism angle near 60°, and that
Size: 1961px × 1274px
Photo credit: © Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorun, bookcentury1800, bookdecade1870, booksubjectscience
