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Na(Ca,Na)2Mg5Si8O22(OH)2
Monoclinic
Richterite is a rare amphibole locally; it is known from only one assemblage. The original report was by Foshag (1936), who described it as a zincian amphibole.
Franklin richterite occurs as euhedral crystals, up to 4 x 1 cm. It is very dark green to nearly black, with vitreous luster, and normal amphibole prismatic cleavages. It is biaxial, negative, with a = 1.665, b = 1.673, and g = 1.676; dispersion is strong; and the pleochroism is distinct, as given by Foshag (1936).
Richterite is a sodium calcium magnesium silicate hydroxide mineral of the amphibole group. Foshag reported an analysis with considerably more Al2O3 than the writer has obtained for identical specimens. Several analyses are presented in Table 12; total Fe has been calculated here as FeO, although part may be ferric (Foshag, 1936). Some Franklin richterites have compositions near a midmember with richterite:winchite near 1:1.
Richterite has been found only with bannisterite, which was known to Foshag (1936) as a variety of ganophyllite. In this assemblage it occurs as prominent crystals, in both a feldspar matrix and within the brown platy bannisterite.
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| Copyright © 1995 by Pete J. Dunn |
Website
by Herb Yeates
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