Elements of mineralogy, crystallography and blowpipe analysis from a practical standpoint .. . Bilin, Boh. Herrengrund. Crystallization.—Orthorhombic. Axes = : i Occasionally simple crystals. Fig. 522, with acute domes. CALCIUM AND MAGNESIUM MINERALS. 311 and pyramids such as e = ao and Fig- S26. s = ^a:~b:6c. These grade into needle-Hkeforms, Fig. 526. More frequently twinned,with twin plane m, giving prisms with pseudo-hexagonal cross sections, Fig. 524 and 525. Angles are: mm = 116° 12; dd = 108°27; vv = 49 39. Optically —. Axial plane a. Acute bi-sectrix no
Elements of mineralogy, crystallography and blowpipe analysis from a practical standpoint .. . Bilin, Boh. Herrengrund. Crystallization.—Orthorhombic. Axes = : i Occasionally simple crystals. Fig. 522, with acute domes. CALCIUM AND MAGNESIUM MINERALS. 311 and pyramids such as e = ao and Fig- S26. s = ^a:~b:6c. These grade into needle-Hkeforms, Fig. 526. More frequently twinned,with twin plane m, giving prisms with pseudo-hexagonal cross sections, Fig. 524 and 525. Angles are: mm = 116° 12; dd = 108°27; vv = 49 39. Optically —. Axial plane a. Acute bi-sectrix normal to c. Axial angle for yellow light, 2E = 30° 54. Cumberland. Physical Characters. H., to 4. Sp. gr., to Lustre, vitreous. Translucent or transparent. Streak, white. Tenacity, brittle. Color, white, violet, yellow, pale green. Cleavage.—Parallel to brachy pinacoid, prism, and brachy dome. Before Blowpipe, Etc.—Infusible, colors flame red. In closedtube decrepitates, loses weight and falls to pieces. With hydro-chloric acid, dissolves with rapid effervescence. Similar Species.—Needle crystals differ from those of natro-lite in the terminations. Strontianite and witherite have higherspecific gravity and are
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