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Eggletonite, the Na analogue of ganophyllite

Published online by Cambridge University Press:  05 July 2018

Donald R. Peacor ,
Pete J. Dunn  and
William B. Simmons
Donald R. Peacor
Affiliation:
Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109
Pete J. Dunn
Affiliation:
Department of Mineral Sciences, Smithsonian Institution, Washington, DC 20560
William B. Simmons
Affiliation:
Department of Earth Sciences, University of New Orleans, New Orleans, Louisiana 70148
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Abstract

Eggletonite is a new mineral, the Na analogue of ganophyllite. Type material has composition

(Na0.82K0.40Ca0.39□0.39)Σ2.00 (Mn6.61Zn0.08Mg0.16Fe0.61Al0.56)Σ8.02 (Si10.33Al1.67)Σ12.00[(O28.92(OH)3.08]Σ32.00 (OH)4.00·10.66H2O.

It occurs as prismatic crystals elongated along [100] in miarolitic cavities in nepheline syenite at the Big Rock Quarry, Little Rock, Arkansas. Single-crystal X-ray diffraction data are consistent with space group I2/a or Ia; a = 5.554, b = 13.72, c = 25.00Å, β = 93.95° Z = 2; this is equivalent to the substructure of ganophyllite. Physical properties include cleavage: {001} perfect; colour: dark brown; translucent; streak: light brown; hardness (Mohs): 3–4; brittle; observed density 2.76, calculated density 2.76 g/cm3. Optically, eggletonite is biaxial negative, with optical parameters 2Vα = 9(3)° r < ν, weak; indices of refraction α = 1.566(2), β = 1.606(2), γ = 1.606(2); pleochroism is very weak, γ ≃ β > α; α = pale brown to colourless, β ≃ γ = pale yellow brown. Principal lines in the X-ray powder diffraction pattern are (d, I/Io): 12.4, 100; 3.45, 15; 3.13, 30; 2.854, 15; 2.691, 25; 2.600, 20; 2.462, 20; 2.387, 15. The name is in honour of Dr Richard A. Eggleton, Australian National University.

Type
Research Article
Information
Mineralogical Magazine , Volume 48 , Issue 346 , March 1984 , pp. 93 - 96
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1984

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References

Dunn, P. J., Leavens, P. B., Norberg, J. A., and Ramik, R. A. (1981) Am. Mineral. 66, 1063.7Google Scholar
Dunn, P. J., Peacor, D. R., Nelen, J. A., and Ramik, R. A. (1983) Mineral. Mag. 47, 563–6.CrossRefGoogle Scholar
Kato, T. (1980) Mineral. J. (Japan). 10, 1–13.CrossRefGoogle Scholar
Threadgold, I. (1979) Mineral. Soc. New South Wales and MineraL Soc. Victoria seminar.Google Scholar