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3CaAl2Si2O8.CaCO3
Tetragonal
Scapolites from Franklin were known to Nuttall (1822) and Nason (1890b). The extant data were summarized by Palache (1935) and Frondel (1972), but are very sparse. There exists a substantial literature on the alteration products of scapolite, once named algerite and kembleite; these were the subject of numerous discussions by Hunt (1849, 1850, 1854), Crossley (1850), Jackson (1850c), and Dana (1853, 1854). Local scapolites are mostly calcium-rich and are the meionite member of the scapolite group.
Fine meionite crystals occur in stout prisms up to 8x10 cm, but have not been studied. Franklin meionites are generally colorless to light yellow or light green; fine-grained violet material is also known. The luster is vitreous; cleavages are good to imperfect; and it is fluorescent in longwave ultraviolet with red, pink, orange, and yellow response colors (Bostwick, 1982).
Meionite is a calcium sodium aluminum silicate carbonate mineral of the scapolite group. The chemical compositions of some local scapolites were reported by Frondel (1972) to be intermediate between those of marialite and meionite, a result confirmed by Kearns (1977) for scapolites in general from the Franklin Marble in New York. The meionite designation used here is based on numerous partial analyses by the writer. The preponderance of Franklin scapolites contain from 50-64 mole % meionite. Marialite occurs here as well, but is rare.
Meionite is moderately common throughout the northern part of the Franklin Marble in New York (Kearns, 1977) and in the Franklin area. In addition to isolated occurrences within the Franklin Marble, it is found at marble contacts with the Franklin orebody.
Local meionite is associated with calcite, microcline, molybdenite, graphite, garnet, phlogopite, titanite, spinel (Figure 22-43), and other species. Most notable are rare, fine pseudomorphs in which 5 cm scapolite crystals are replaced by bright green epidote; this material is associated with a dark colored, unanalyzed garnet. Much work remains to be done. A non-type specimen labeled algerite, and fitting the description of that material, was found by the writer to be largely mica. Unanalyzed scapolite is known from the Sterling Hill orebody.
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| Copyright © 1995 by Pete J. Dunn |
Website
by Herb Yeates
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