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Kyawthuite, Bi^(3+)Sb^(5+)O_4, a new gem mineral from Mogok, Burma (Myanmar)

Kampf, Anthony R. and Rossman, George R. and Ma, Chi and Williams, Peter W. (2017) Kyawthuite, Bi^(3+)Sb^(5+)O_4, a new gem mineral from Mogok, Burma (Myanmar). Mineralogical Magazine, 81 (3). pp. 477-484. ISSN 0026-461X.

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Kyawthuite, Bi^(3+)Sb^(5+)O_4, is a new gem mineral found as a waterworn crystal in alluvium at Chaung-gyi-ah-le-ywa in the Chaung-gyi valley, near Mogok, Burma (Myanmar). Its description is based upon a single sample, which was faceted into a 1.61-carat gem. The composition suggests that the mineral formed in a pegmatite. Kyawthuite is monoclinic, space group I2/c, with unit cell dimensions a = 5.4624(4), b = 4.88519(17), c = 11.8520(8) Å, β = 101.195(7)°, V = 310.25(3) Å^3 and Z = 4. The colour is reddish orange and the streak is white. It is transparent with adamantine lustre. The Mohs hardness is 5½. Kyawthuite is brittle with a conchoidal fracture and three cleavages: {001} perfect, {110} and {110} good. The measured density is 8.256(5) g cm^(–3) and the calculated density is 8.127 g cm^(–3). The mineral is optically biaxial with 2V = 90(2)°. The predicted indices of refraction are α = 2.194, β = 2.268, γ = 2.350. Pleochroism is imperceptible and the optical orientation is X = b; Y ≈ c; Z ≈ a. Electron microprobe analyses, provided the empirical formula (Bi^(3+)_(0.82)Sb^(3+)_(0.18))_(Σ1.00)( Sb^(5+)_(0.99)Ta^(5+)_(0.01))_(Σ1.00)O_4. The Raman spectrum is similar to that of synthetic Bi^(3+)Sb^(5+)O_4. The infrared spectrum shows a trace amount of OH/H_2O. The eight strongest powder X-ray diffraction lines are [d_(obs) in Å(I)(hkl)]: 3.266(100)(112), 2.900(66)(112), 2.678(24)(200), 2.437(22)(020, 14), 1.8663(21)(024), 1.8026(43)(16,220,204), 1.6264(23)(224,116) and 1.5288(28)(312, 32). In the crystal structure of kyawthuite (R_1 = 0.0269 for 593 reflections with F_o > 4σF), Sb^(5+)O_6 octahedra share corners to form chequerboard-like sheets parallel to {001}. Atoms of Bi^(3+), located above and below the open squares in the sheets, form bonds to the O atoms in the sheets, thereby linking adjacent sheets into a framework. The Bi^(3+) atom is in lopsided 8 coordination, typical of a cation with stereoactive lone electron pairs. Kyawthuite is isostructural with synthetic β-Sb_2O_4 and clinocervantite (natural β-Sb_2O_4).

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Rossman, George R.0000-0002-4571-6884
Alternate Title:Kyawthuite, Bi3+Sb5+O4, a new gem mineral from Mogok, Burma (Myanmar)
Additional Information:© 2017 The Mineralogical Society. Received 4 January 2016; Accepted 21 March 2016. Comments by an anonymous reviewer and Structures Editor Peter Leverett are appreciated. Ken Scarratt is thanked for providing information on the examination of the kyawthuite gem by the Gemological Institute of America (GIA) Laboratory in Bangkok. Uwe Kolitsch and Harald Schillhammer are thanked for comments that led us to provide more accurate and detailed locality information. The spectroscopic and EPMA analyses at Caltech were supported by NSF grants EAR-0947956 and EAR-0318518. The remainder of this study was funded by the John Jago Trelawney Endowment to the Mineral Sciences Department of the Natural History Museum of Los Angeles County.
Funding AgencyGrant Number
Natural History Museum of Los Angeles County John Jago Trelawney EndowmentUNSPECIFIED
Subject Keywords:yawthuite; new mineral; gemstone; antimonate; crystal structure; Mogok, Burma (Myanmar)
Record Number:CaltechAUTHORS:20170411-075819920
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Official Citation:Kyawthuite, Bi3+Sb5+O4, a new gem mineral from Mogok, Burma (Myanmar) Anthony R. Kampf, George R. Rossman, Chi Ma, Peter A. Williams Mineralogical Magazine Jun 2017, 81 (3) 477-484; DOI: 10.1180/minmag.2016.080.102
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:76496
Deposited By: Tony Diaz
Deposited On:11 Apr 2017 17:02
Last Modified:11 Apr 2017 17:02

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