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BaBe2Si2O7
Orthorhombic, Pnma, a = 9.80, b = 11.65, c = 4.71
Å, Z = 4.
Barylite was found at Franklin in 1929 and described by Palache and Bauer (1930); it had formerly been known only from Långban, Sweden. Additional discussion was given by Palache (1935), and local material was used for the determination of the unit-cell and space group by Smith (1956), as given above. The synthesis of barylite was reported by Ito and Frondel (1966); they also reported X-ray powder data for Franklin barylite. Barylite is not known from Sterling Hill.
Franklin barylite occurs in platy crystals, wholly enclosed in matrix; subparallel masses of crystals up to 10 cm are known. Some crystals are slightly curved and coated with serpentine. Barylite is colorless to gray or grayish white, with vitreous luster, two good cleavages, and a density of 4.07 g/cm3. The high hardness (7) is diagnostic. Optically, Franklin barylite is biaxial, negative, 2V = 70o, a = 1.695, b = 1.702, and g = 1.708; the cleavages are normal to beta and gamma. Barylite is difficult to identify by visual examination.
The fluorescence in ultraviolet is deep violet and is faint using commercially available lamps. The vivid fluorescence reported by Palache and Bauer (1930) is seen only under the older, iron-spark fluorescence-generating units, no longer in use and difficult to find except in the Franklin area. Barylite’s fluorescence was long a subject of local controversy (Gaines and Bostwick, 1993). Many specimens of bright-blue-fluorescent margarosanite in microcline were misidentified as barylite between 1930 and 1990. A bluish-white thermoluminescence was noted by Northup and Lee (1940).
Barylite is a barium beryllium silicate mineral. Microprobe analyses of Franklin material by this writer were published by Gaines and Bostwick (1993). The composition of barylite is remarkably uniform and conforms closely to the theoretical composition. Solid solution is quite limited; only Pb substitutes for Ba to any appreciable extent. Several representative analyses (of samples #C6224 and #142815, respectively) yielded SiO2 37.4, 37.2, BaO 45.9, 44.6, PbO 1.5, 2.6, with Be calculated at 15.5, 15.5, totals = 100.3 and 99.9 wt. percent. Spectrographic analysis by Northup and Lee (1940) showed 0.0x Mg and only traces of Mn, Fe, Al, Pb, Zn, and Sn, given in order of decreasing concentration.
Barylite was first found on the picking table, and later was found in 960 pillar, 20 feet below the 400 level and 15 feet from the hanging wall, in the Franklin Mine. Palache and Bauer (1930) described barylite occurring with hedyphane, willemite, copper, brown and gray calcite, and white curved calcite. They noted that barylite is more or less brecciated and some is coated with thin films of serpentine. This is the only assemblage known to the writer. This assemblage of copper, curved white calcite, and serpentine stringers and films is quite recognizable once seen and was described in excruciating and superb detail by Gaines and Bostwick (1993). Barylite is a rare mineral at Franklin.
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| Copyright © 1995 by Pete J. Dunn |
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