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Noelbensonite, a new BaMn silicate of the lawsonite structure type, from Woods Mine, New South Wales, Australia

Y. Kawachi, D. S. Coombs and H. Miura
Noelbensonite, a new BaMn silicate of the lawsonite structure type, from Woods Mine, New South Wales, Australia
Mineralogical Magazine (April 1996) 60 (2): 369-374

Abstract

Noelbensonite, a new mineral, is the barium manganese analogue of lawsonite. It is described from the Woods ornamental rhodonite mine, 30 km NNE of Tamworth, New South Wales, Australia, where it occurs as aggregates of blocky to sometimes lamellar crystals ranging from a few micrometres to (rarely) 100 mu m in length. It replaces NaMn amphibole, namansilite, and pectolite, and also occurs as tiny monomineralic veinlets 0.05-0.25 mm thick. Rare euhedral crystals are dominated by {100} and {011}, with (011) ^ (011(bar)) = 68 degrees . The mineral is orthorhombic, space group apparently Cmcm; a = 6.325(1), b = 9.120(1), c = 13.618(1) Aa, V = 785.6(1) Aa (super 3) , with a : b : c = 0.694 : 1 : 1.493. Noelbensonite is brittle, fracture irregular, Mohs hardness about 4, cleavage and twinning not observed, colour dark brown, streak paler yellow-brown, lustre earthy on some veinlet surfaces to brilliantly vitreous, calculated density 3.87 g/cm (super 3) , refractive indices alpha = 1.82(1),beta (calculated from 2V) = 1.835(10), gamma = 1.85(1), biaxial negative 2V (sub alpha ) = 46 degrees (3 degrees ), strong dispersion r > v, straight extinction to plane of flattening, {100}, alpha parallel to c, beta parallel to b, gamma parallel to a with pleochroism in very thin sections: alpha = orange yellow, beta = orange, gamma = brownish orange, absorption gamma > beta <-->p; alpha . The average of 23 electron microprobe analyses (wt.%) is SiO (sub 2) 26.02, Al (sub 2) O (sub 3) 0.17, TiO (sub 2) 0.01, Fe (sub 2) O (sub 3) 0.19, Mn (sub 2) O (sub 3) 34.76, CaO 0.31, Na (sub 2) O 0.14, BaO 29.08, SrO 1.51, H (sub 2) O (sub calc) 7.87, total 100.06, leading to the simplified formula BaMn (sub 2) (super 3+) [Si (sub 2) O (sub 7) ](OH) (sub 2) .H (sub 2) O. Up to 15% Sr and 9% Ca substitute for Ba in the large-cation sites. The strongest lines in the X-ray powder diffraction pattern are [(I (sub obs) ) d (sub obs) /Aa hkl] (100) 4.85 111; (50) 4.557 020; (59) 4.322 021; (77) 3.416 113,004; (80) 2.869 202; (47) 2.849 114; (82) 2.729 024; (45) 2.543 132; (48) 2.428 222; (38) 2.255 223,041. The name is for William Noel Benson (1885-1957), in honour of his classic researches in the New England Fold Belt and of his tenure of the Chair of Geology at the University of Otago.


ISSN: 0026-461X
Serial Title: Mineralogical Magazine
Serial Volume: 60
Serial Issue: 2
Title: Noelbensonite, a new BaMn silicate of the lawsonite structure type, from Woods Mine, New South Wales, Australia
Affiliation: University of Otago, Geology Department, Dunedin, New Zealand
Pages: 369-374
Published: 199604
Text Language: English
Publisher: Mineralogical Society, London, United Kingdom
References: 11
Accession Number: 1996-052572
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: 3 tables
S31°07'00" - S31°07'00", E150°56'60" - E150°56'60"
Secondary Affiliation: Hokkaido University, JPN, Japan
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Mineralogical Society of Great Britain and Ireland
Update Code: 199617
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