Deynekoite, Ca9□Fe3+(PO4)7 – a new mineral of the merrillite group from phosphide-bearing contact facies of paralava, Hatrurim Complex, Daba-Siwaqa, Jordan
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Galuskin_deynekoite_ca9-fe3po47_a_new_mineral_of_the_merrillite_group_from_phosphide_bearing.pdf (2.17 MB)
0000-0002-7018-527X Date
2023
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Cambridge University Press
Abstract
Deynekoite, Ca9☐Fe3+(PO4)7 (R3c, a = 10.3516(3)Å, c = 37.1599(17)Å, V = 3448.4(3)Å3, Z = 6), a new mineral of the merrillite group was found in a contact facies of paralava of the Hatrurim Complex in the Daba-Siwaqa pyrometamorphic rock field, Jordan. The paralava, consisting of diopside, tridymite, anorthite, wollastonite and fluorapatite, is enriched in Fe-bearing phosphides and phosphates at the contact with the altered country rock. Cristobalite overgrowing tridymite has a texture of the fish scales-type indicating that temperature of paralava could have reached 1500C. Deynekoite with empirical formula (Ca8.90Na0.11K0.02)9.03(Fe3+0.62 Mg0.30Al0.05)0.97P6.98V5+0.05O27.70(OH)0.30 forms transparent, light-yellow or light-brown grains up to 30-40 m in size. Microhardness of deynekoite VHN25 = 319(29) kg/mm2, that coresponds to the Mohs hardness = 4.5. Its density was calculated as 3.09 g·cm-3 on the basis of its empirical composition and structural data. Deynekоite is uniaxial (−), its refractive indices are ω = 1.658(3), ε = 1.652(3) (λ = 589 nm), and pleochroism is not observed. The formation of phosphides on the boundary of the paralava and country rock is connected with carbothermal reductive reactions and realized at temperatures above 1300С. With decreasing temperature and increasing oxygen activity, phosphides are replaced by Fe2+-bearing phosphates. Deynekoite, which contains Fe3+ (substituting for Fe2+-phosphates) and a small amount of water, formed at temperatures of 600–800C.
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Galuskin, E.V. et al. (2023) ‘Deynekoite, Ca9□Fe3+(PO4)7 – a new mineral of the merrillite group from phosphide-bearing contact facies of paralava, Hatrurim Complex, Daba-Siwaqa, Jordan’, Mineralogical Magazine, 87(6), pp. 943–954. doi:10.1180/mgm.2023.71.