Abstract

Moraskoite, a new natural phosphate of composition Na2Mg(PO4)F, has been found in the Morasko IAB-MG iron meteorite. The new phosphate occurs in a graphite-troilite inclusion enclosed in a kamacite-taenite matrix. Associated minerals in the inclusions are chlorapatite, buchwaldite, brianite, merrillite, a new phosphate phase of composition Na4MgCa3(PO4)4, chromite, enstatite (bronzite), kosmochlor, kosmochlor–augite, olivine, albite, orthoclase, quartz, cohenite, schreibersite, nickelphosphide, altaite, pyrrhotite, sphalerite, daubreelite, djerfischerite, whitlockite and native Cu. The inclusions are rimmed by a schreibersite-cohenite halo. Moraskoite forms aggregates up to 1.5 mm in size, with individual grains 20–300 μm across. It is colourless and transparent, with a white streak and vitreous lustre; fluorescence is weak blue in ultraviolet radiation (254 and 360 nm); hardness is 4–5; it has irregular, conchoidal fracture and cleavage is rarely observed. Calculated density (using the empirical formula) is 2.925 g cm−3. The moraskoite structure (Pbcn, a = 5.2117(10), b = 13.711(3), c = 11.665(2) Å, V = 833.6(3) Å3 and Z = 8) is similar to that of its synthetic analogue. The strongest diffraction lines of the moraskoite powder diffraction pattern are as follows (dhkl, I): 3.909(75), 3.382(52), 2.955(90), 2.606(100), 2.571(96), 2.545(68), 1.691 (67). In the Raman spectrum, the following characteristic bands are distinguished (cm−1, strong bands bold): 1114, 1027, 962, 589, 438, 336, 308, 279, 262, 244, 193, 184, 147 and 131. The Raman data prove the absence of H2O and CO2. Moraskoite is interpreted as being a primary phosphate, which crystallized together with graphite, troilite and other accessories inside the nodule.

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