Goldschmidtite is a new perovskite-group mineral (IMA No. 2018-034) with the ideal formula (K,REE,Sr)(Nb,Cr)O 3 . A single grain of goldschmidtite with a maximum dimension of ∼100 μm was found as an inclusion in a diamond from the Koffiefontein pipe in South Africa. In addition to the dark green and opaque goldschmidtite, the diamond contained a Cr-rich augite (websteritic paragenesis) and an intergrowth of chromite, Mg-silicate, and unidentified K-Sr-REE-Nb-oxide. Geothermobarometry of the augite indicates that the depth of formation was ∼170 km. The chemical composition of gold-schmidtite determined by electron microprobe analysis (n = 11, WDS, wt%) is: Nb 2 O 5 44.82, TiO 2 0.44, ThO 2 0.10, Al 2 O 3 0.35, Cr 2 O 3 7.07, La 2 O 3 11.85, Ce 2 O 3 6.18, Fe 2 O 3 1.96, MgO 0.70, CaO 0.04, SrO 6.67, BaO 6.82, K 2 O 11.53, total 98.53. The empirical formula (expressed to two decimal places) is (K 0.50 La 0.15 Sr 0.13 Ba 0.09 Ce 0.08 ) Σ0.95 (Nb 0.70 Cr 0.19 Fe 0.05 Al 0.01 Mg 0.04 Ti 0.01 ) Σ1.00 O 3 . Goldschmidtite is cubic, space group Pm3m, with unit-cell parameters: a = 3.9876(1) Å, V = 63.404(6) Å3, Z = 1, resulting in a calculated density of 5.32(3) g/cm3. Goldschmidtite is the K-analog of isolueshite, (Na,La)NbO 3 . Raman spectra of goldschmidtite exhibit many second-order broad bands at 100 to 700 cm–1 as well as a pronounced peak at 815 cm–1, which is possibly a result of local ordering of Nb and Cr at the B site. The name goldschmidtite is in honor of the eminent geochemist Victor Moritz Goldschmidt (1888–1947), who formalized perovskite crystal chemistry and identified KNbO 3 as a perovskite-structured compound.