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Mineralogical ClassificationIMA 2014-097 = jeffbenite

30th Nov 2016 05:02 UTCMarco E. Ciriotti Manager

Reference:

▪ Nestola, F., Burnham, A.D., Peruzzo, L., Tauro, L., Alvaro, M., Walter, M.J., Gunter, M., Kohn, S.C. (2016): Tetragonal Almandine-Pyrope Phase, TAPP: finally a name for it, the new mineral jeffbenite. Mineralogical Magazine, 80, 1219-.1232.

Abstract:

Jeffbenite, ideally Mg3Al2Si3O8, previously known as tetragonal-almandine-pyrope-phase ("TAPP"), has been characterized as a new mineral from an inclusion in an alluvial diamond from São Luiz river, Juina district of Mato Grosso, Brazil. Its density is 3.576 g/cm3 and its microhardness is about 7. Jeffbenite is uniaxial (-) with refractive indexes ω = 1.733(5) and ε = 1.721(5). The crystals are in general transparent emerald green. Its approximate chemical formula is (Mg2.62Fe2+ 0.27)(Al1.86Cr0.16)(Si2.82Al0.18)O12 with very minor amounts of Mn, Na and Ca. Laser ablation ICP-MS showed that jeffbenite has very low concentration of trace elements. Jeffbenite is tetragonal with space group I42d , cell edges being a = 6.5231(1) Å and c = 18.1756(3) Å. The main diffraction lines of the powder diagram are [d (in Å), intensity, hkl]: 2.647, 100, 2 0 4; 1.625, 44, 3 2 5; 2.881, 24, 2 1 1; 2.220, 19, 2 0 6; 1.390, 13, 4 2 4; 3.069, 11, 2 0 2; 2.056, 11, 2 2 4; 1.372, 11, 2 0 12. The structural formula of jeffbenite can be written as (M1)(M2)2(M3)2(T1)(T2)2O12 with M1 dominated by Mg, M2 dominated by Al, M3 dominated again by Mg and both T1 and T2 almost fully occupied by Si. The two tetrahedra do not share any oxygen with each other (i.e. jeffbenite is classified as an orthosilicate). Jeffbenite was approved as a new mineral by the IMA Commission on New Minerals and Mineral Names with the code IMA 2014-097. Its name is after Jeffrey W. Harris and Ben Harte, two world-leading scientists in diamond research. The petrological importance of jeffbenite is related to its very deep origin, which may allow its use as a pressure marker for detecting super-deep diamonds. Previous experimental work carried out on a Ti-rich jeffbenite establishes that it can be formed at 13 GPa and 1700 K as maximum P-T conditions.

30th Nov 2016 09:24 UTCErik Vercammen Expert

Jeffbenite, ideally Mg3Al2Si3O8: shouldn't it be O12?

1st Dec 2016 09:43 UTCChris Stanley Expert

Yes, well spotted Eric.

bws

Chris S

1st Dec 2016 13:36 UTCLuís Martins 🌟

Can you send me the paper Marco?

1st Dec 2016 14:55 UTCMarco E. Ciriotti Manager

Done. Enjoy!

7th Dec 2016 16:32 UTCUwe Kolitsch Manager

"... space group I42d"

Should this read I-42d?

7th Dec 2016 19:46 UTCMarco E. Ciriotti Manager

I-42d

7th Dec 2016 19:46 UTCMarco E. Ciriotti Manager

I-42d

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