. Bulletin - New York State Museum. Science. LAJ Fig. 101 Fig. 102 Fig. 103 this axis. The third order pyramid and prism, indicated in plan in fig. 102, are of frequent occurrence in this group, as well as the pyramids and prisms of the first and second order described above. The crystal of vanadinite shown in fig. 103 illustrates a combi nation of pyramidal forms. Apatite and pyromorphite are com- mon minerals in this group. B Rhombohedral division The groups which come under this division differ from the hexagonal forms hitherto discussed in the essential feature of a vertical axis of trigon
. Bulletin - New York State Museum. Science. LAJ Fig. 101 Fig. 102 Fig. 103 this axis. The third order pyramid and prism, indicated in plan in fig. 102, are of frequent occurrence in this group, as well as the pyramids and prisms of the first and second order described above. The crystal of vanadinite shown in fig. 103 illustrates a combi nation of pyramidal forms. Apatite and pyromorphite are com- mon minerals in this group. B Rhombohedral division The groups which come under this division differ from the hexagonal forms hitherto discussed in the essential feature of a vertical axis of trigonal symmetry which gives to the Termina- tion of rhombohedral crystals a trigonal as dis- tinct from a hexagonal aspect. Compare fig. 104, which shows a termination of a rhombo- hedral crystal, with the hexagonal terminations shown in fig. 91 and 101. Compare also model 8 with model 7. Rhombohedral group Forms in this group are characterized by a vertical axis of trigonal symmetry and three horizontal axes <»f binary sym- metry, these ;ix«-s being identical with the crystallographic axes. They are also symmetric to ihr<-<- planes which interseel in the vertical axis ;is shown in ti^. Pig. 1'4. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original New York State Museum; New York State Museum. Albany : New York State Education Dept
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectscience, bookyear1887
