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Potassic-jeanlouisite from Leucite Hill, Wyoming, USA, ideally K(NaCa)(Mg4Ti)Si8O22O2: the first species of oxo amphibole in the sodium–calcium subgroup

Published online by Cambridge University Press:  28 June 2019

Roberta Oberti Open the ORCID record for Roberta Oberti [Opens in a new window] ,
Massimo Boiocchi ,
Frank C. Hawthorne ,
Giancarlo Della Ventura  and
Gunnar Färber
Roberta Oberti*
Affiliation:
CNR-Istituto di Geoscienze e Georisorse, Sede secondaria di Pavia, via Ferrata 1, I-27100 Pavia, Italy
Massimo Boiocchi
Affiliation:
Centro Grandi Strumenti, Università di Pavia, via Bassi 21, I-27100 Pavia, Italy
Frank C. Hawthorne
Affiliation:
Department of Geological Sciences, University of Manitoba, Winnipeg, Manitoba, R3T 2N2, Canada
Giancarlo Della Ventura
Affiliation:
Dipartimento di Scienze, Università di Roma Tre, largo S. Leonardo Murialdo 1, I-00146, Rome, Italy INFN-LNF, Via E. Fermi 40, I-00044 Frascati, Italy
Gunnar Färber
Affiliation:
Bornsche Strasse 9, D 39326 Samswegen, Germany
*
*Author for correspondence: Roberta Oberti, Email: [email protected]
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Abstract

Potassic-jeanlouisite, ideally K(NaCa)(Mg4Ti)Si8O22O2, is the first characterised species of oxo amphibole related to the sodium–calcium group, and derives from potassic richterite via the coupled exchange CMg–1W${\rm OH}_{{\rm \ndash 2}}^{\ndash}{} ^{\rm C}{\rm Ti}_1^{{\rm 4 +}} {} ^{\rm W}\!{\rm O}_2^{2\ndash} $. The mineral and the mineral name were approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification, IMA2018-050. Potassic-jeanlouisite was found in a specimen of leucite which is found in the lava layers, collected in the active gravel quarry on Zirkle Mesa, Leucite Hills, Wyoming, USA. It occurs as pale yellow to colourless acicular crystals in small vugs. The empirical formula derived from electron microprobe analysis and single-crystal structure refinement is: A(K0.84Na0.16)Σ1.00B(Ca0.93Na1.02Mg0.04${\rm Mn}_{{\rm 0}{\rm. 01}}^{2 +} $)Σ2.00C(Mg3.85${\rm Fe}_{{\rm 0}{\rm. 16}}^{2 +} $Ni0.01${\rm Fe}_{{\rm 0}{\rm. 33}}^{3 +} {\rm V}_{{\rm 0}{\rm. 01}}^{3 +} $Ti0.65)Σ5.01T(Si7.76Al0.09Ti0.15)Σ8.00O22W[O1.53F0.47]Σ2.00. The holotype crystal is biaxial (–), with α = 1.674(2), β = 1.688(2), γ = 1.698(2), 2Vmeas. = 79(1)° and 2Vcalc. = 79.8°. The unit-cell parameters are a = 9.9372(10), b = 18.010(2), c = 5.2808(5) Å, β = 104.955(2)°, V = 913.1(2) Å3, Z = 2 and space group C2/m. The strongest eight reflections in the powder X-ray pattern [d values (in Å) (I) (hkl)] are: 2.703 (100) (151); 3.380 (87) (131); 2.541 (80) ($\bar 2$02); 3.151 (70) (310); 3.284 (68) (240); 8.472 (59) (110); 2.587 (52) (061); 2.945 (50) (221,$\bar 1$51).

Keywords

potassic-jeanlouisitenew amphibole specieselectron-microprobe analysisoptical propertiespowder-diffraction patterncrystal-structure refinementLeucite HillsWyomingUSA
Type
Article
Information
Mineralogical Magazine , Volume 83 , Issue 4 , August 2019 , pp. 587 - 593
Copyright
Copyright © Mineralogical Society of Great Britain and Ireland 2019 

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Footnotes

Associate Editor: Anthony R Kampf

References

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