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Czochralskiite, Na4Ca3Mg(PO4)4, is the second new phosphate mineral found in the Morasko IAB-MG iron meteorite. This very rare mineral occurs in phosphate inclusions (nodules) with graphite rims enclosed in the kamacite–taenite matrix of the meteorite. Almost thirty mineral species have been reported from this meteorite (most from various inclusions), including six, possibly eight phosphates (fluorapatite, buchwaldite, brianite, merrillite, moraskoite Na2Mg(PO4)F, chlorapatite? and whitlockite?), and schreibersite, chromite, enstatite (‘bronzite’), kosmochlor, kosmochlor–augite, olivine, albite, orthoclase, quartz, cohenite, nickelphosphide, altaite, troilite, pyrrhotite, sphalerite, daubreelite, djerfisherite, and native Cu. Czochralskiite forms xenomorphic, usually oval grains and amoeboid aggregates, between 0.1 and 0.5 mm in size. It is colourless and transparent, with white streak and vitreous lustre; it shows no fluorescence, it is biaxial (+): α = 1.608(2), β = 1.611(2), γ = 1.616(2); α = a, β = b, γ = c; 2V (meas.) = 70° (10), 2V (calc.) = 76°; the dispersion is very weak; Mohs’ hardness is 4–5; the fracture is irregular, conchoidal, and no cleavage was observed. The mean of twelve electron-microprobe analyses is (wt%): P2O5 46.28, CaO 27.59, Na2O 20.04, MgO 6.21, FeO 0.32, MnO 0.16, K2O 0.09, total 100.69, leading to the empirical formula Na3.97Ca3.02Mg0.95Mn2+0.01K0.01Fe2+0.03(P4.00O16). The calculated density based on the empirical formula and the single-crystal structural data is 3.148 g · cm−3. The structure of czochralskiite [Pnma, a = 17.9230(2), b = 10.7280(2), c = 6.7794(1) Å, V = 1303.53(3)Å3, Z = 4] is of the glaserite-type and related to that of buchwaldite and brianite. The strongest diffraction lines of the calculated czochralskiite powder diffraction pattern are [dhkl (I)]: 3.802(48), 3.728(31), 2.726(100), 2.679(63), 2.602(83), 1.901 (44). The Raman spectrum shows the following characteristic bands (cm−1, strong bands underlined): 1119, 1167, 1053, 1039, 1022, 1011, 986, 974, 966, 606, 585, 578 and 441. The Raman data show the absence of H2O and CO2. Czochralskiite is interpreted as a primary phosphate, which crystallized together with graphite and other phosphates inside the nodules. The mineral name honours Jan Czochralski (1885–1953), Polish chemist, crystallographer and metallurgist.