Kopernikite, K(Ti7Cr3+)O16 – a new mineral belonging to the priderite group with a hollandite-type structure, was discovered within a graphite–troilite nodule in the Morasko iron meteorite of the IAB-MG type. This meteorite fell in the territory of modern-day Poland around 5000 years ago. Kopernikite is confined to the external graphite zone of the nodule and intergrows with fluorapatite. The kopernikite structure was refined (I4/m, a = 10.0955(5) Å, c = 2.9534(2) Å, V = 301.01(4) Å3 and Z =1) for the grains with the composition (K1.12Ba0.23Ca0.03Na0.03)Σ1.42(Ti4+6.48Cr3+1.46Fe2+0.01 Al0.01)Σ7.96O16 based on 375 unique reflections to R1 value of 0.018. The colour of kopernikite changes from dark green in massive grains to yellow–green in thin grains, and the streak is light green. The mineral has a vitreous lustre and a hardness of ∼5.5 on the Mohs scale, as calculated on the basis of microhardness VHN25 = 646(17) kg/mm2. The Raman spectrum of kopernikite is similar to that of priderite. Kopernikite crystallised from drops of phosphate melt simultaneously with fluorapatite at a temperature of 1000°C, due to the local enrichment of the melt with K, Ba, Ti and Cr. The increased amount of tunnel cations in the kopernikite structure (∼1.4–1.5 apfu), as calculated from microprobe analyses, exceeds the theoretically possible value of 1.33 apfu for minerals of the priderite group. This increase can be attributed to formation of kopernikite under the increased pressure, as well as artefacts that appear when the mineral composition is measured using a microprobe analyser.

Magnetite grains with exsolved ilmenite lamellae may be replaced by pyrite or carbonate in phlogopitites of the Catalão I carbonatite complex, Goiás State, Brazil. The ilmenite is transformed in part to priderite and sometimes to rutile. Priderite occurs as small anhedral grains (< 0.2mm) or composite crystals associated with ilmenite and rutile. Chalcopyrite, magnetite, monazite, and pyrochlore also occur inside the area of original magnetite grains. The priderite belongs to the K2FeTi7O16-BaFeTi7O16 series with K/(K + Ba) ranging from 1.0 to 0.53. The highest contents for other elements are: V2O3 2.65, Cr2O3 4.1, and Nb2O5 1.98 wt.%. Priderites associated with magnetite have the highest V, Cr, and Nb contents whereas others have the highest Ba content. Zoning characterized by K-Ba substitution is patchy but always present. V-and Cr-poor priderites are similar in composition to priderites from lamproites, and the V- and Cr-rich ones are compositionally similar to hollandite-group minerals found in kimberlites.

Compositional data are presented for Nb-Ba-K-V titanates from micaceous kimberlite (Star mine, S. Africa). These data significantly extend the previously known range of solid solutions in naturally occurring members of the hollandite group. Two distinct suites of crystals occur. One is a suite of primary groundmass prismatic crystals that are Ba-K-V-rich and represent solid-solutions from the priderite series towards mannardite. The second suite consists of anhedral xenocrysts that are Ba-free. In this suite relatively Nb-rich varieties (>4.0% Nb2O5) represent solid-solution towards a niobian-bearing potassian analogue of mannardite, whereas relative Nb-poor (<3.0% Nb2O5) varieties are Nb-bearing vanadian priderites. These hollandite-group minerals have compositions that differ significantly from priderites found in lamproites.