First Report of Metamict Alluaudite (A Sodium Iron Manganese Phosphate Mineral) from Pisangan, Ajmer District, Rajasthan

Abstract

For the first time we report alluaudite from India, which is metamict and is hosted in a zoned pegmatite, near Pisangan, Ajmer district, Rajasthan. Alluaudites known till date, all over the world, are non-metamict type. Therefore, the alluaudite reported from the area is the first locality in the world for the metamict-type of alluaudite. The most conspicuous features exhibited by the alluaudite are various types of cracks in different directions and shapes, including its isotropic nature. The calculated crystallographic parameters of the reported alluaudite are: a0 = 11.9874 Å, b0 = 12.5144 Å, and c0 = 6.4136 Å, β = 114.240 with unit-cell volume (V) = 877.31 Å3, which are in agreement with the values of alluaudite standard. Geochemical data indicates high content of P (32.30% P2O5), Fe (30.2% Fe2O3), Mn (10.62% MnO), besides Mg (7.71% MgO), Ca (5.60% CaO), Na (3.40% Na2O) and Si (2.30% SiO2), and appreciable amount of water of hydration (3.50% LOI). It is highly radioactive due to uranium (2.28% U3O8) and thorium (185 ppm Th). Calculated structural formula of the alluaudite is Na1+0.59Ca2+0.54Mn2+0.80Mg2+1.02Fe3+2.03Al3+0.037U4+0.043P5+2.45O12. The chondrite-normalised plot shows enrichment of HREE relative to LREE with pronounced negative Eu-anomaly (Eu/Eu* = 0.46). Such a high negative Eu-anomaly suggests extremely fractionated nature of the host pegmatite.

Pegmatites As Decorative and Dimensional Stone Occurring in South-Central Rajasthan, India

“…Because of its compactness and massive nature, this massive pegmatite cannot be exploited to produce quartz, feldspar, or mica. Choudhari (1966), Bhattacharjee (1982Bhattacharjee ( , 1984, Joshi et al (2014), andSingh et al (2016) have studied various aspects of pegmatites, especially mica-bearing pegmatites in the study area, but a detailed study on massive-type of pegmatites for their use as decorative and dimensional stone has not yet been carried out. Thus, this study was taken up to describe field and mineralogical characteristics as well as economic significance of these massive-type pegmatites of the study area.…”