. Bulletin - United States National Museum. Science. 120 121 Figs. 120-121.—Analcite, Challis, Custer County. 120, Simple trapezohedron. 121, Trape- zohedron modified by cube and trisoctahedron appearance. They are for the most part simple trapezohedrons of form q (112), which is a common form for analcite as shown in Figure 120. Occasionally, however, one shows faces of the cube a(100), and of the trigonal trisoctahedron w(233), which though previously known are rare forms on analcite. A modified crystal is illustrated in Figure 121. * Certain very interesting crystals occur between the plate
. Bulletin - United States National Museum. Science. 120 121 Figs. 120-121.—Analcite, Challis, Custer County. 120, Simple trapezohedron. 121, Trape- zohedron modified by cube and trisoctahedron appearance. They are for the most part simple trapezohedrons of form q (112), which is a common form for analcite as shown in Figure 120. Occasionally, however, one shows faces of the cube a(100), and of the trigonal trisoctahedron w(233), which though previously known are rare forms on analcite. A modified crystal is illustrated in Figure 121. * Certain very interesting crystals occur between the plates of the associated argentine calcite. These are attached to the calcite plates by the equatorial plane and, where space was available, have developed completely in their top half. Where the space between the calcite plates was thin the analcites are very mucli flattened and are bounded only on their edges by narrow crystal planes. Both undeformed and greatly flattened crystals are shown attached to calcite in the photograph at the right of Plate 12. These disklike plates may reach 1 cm. in diameter with a thickness of only mm. although most of them are thicker than this, with a smaller diameter. Selected ones of these are ideal thin sections, and show admirably the birefringence and division into sectors. Such a crystal photo-. 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 United States National Museum; Smithsonian Institution; United States. Dept. of the Interior. Washington : Smithsonian Institution Press, [etc. ]; for sale by the Supt. of Docs. , U. S. Govt Print. Off.
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