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The preparation and characterisation of four chromium ore reference materials are described in this paper. The sample material for GCr-1, GCr-3 and GCr-4 was collected from chromite deposits in Tibet, Qinghai province and Inner Mongolia. GCr-2 is a composite sample from GCr-1 and GCr-4. Sample homogeneity was tested by WD-XRF and the relative standard deviations were < 1.0%. An F-test showed that all four materials were homogeneous. Thirteen laboratories involved in the inter-laboratory programme provided 672 determinations (eighteen oxides and elements). Sixteen components were characterised as certified values, of which Cr2O3 ranged from 17.59 to 57.80% m/m. The contents of FeO and CO2 were taken as reference values. [ABSTRACT FROM AUTHOR]