Some of the chemical elements that make up minerals and rocks are necessary for the health of flora, fauna and humans. Cr3+ in low doses is an essential element while Cr6+ is carcinogenic. Some ground and rocks in Slovenia have elevated concentrations of chromium. We have confirmed high concentrations of it in flysch sandstones, eclogite and serpentinite by using X-ray fluorescence (XRF). Analysis has shown that the concentration of chromium in flysch sandstones is between 103 mg/kg and 257 mg/kg, in eclogite it is 431 mg/kg and it is the highest in serpentinite – 5947 mg/kg. All these concentrations exceed the legally permitted limit value for ground 100 mg/kg and in some cases also exceed the critical value 380 mg/kg. Transmitted polarising light microscopy has shown presence of opaque minerals that could be carriers of chromium. Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM/EDS) analysis has confirmed that chromium is bound as chromite and Cr-spinels. In serpentinite, chromium is bound in Cr-spinels, olivine and magnetite; it is also bound as magnetite in eclogite. Based on the low concentration of TiO2 and high concentration of Cr/(Cr+Al) the spinels have source in the mantel peridotites though it is possible those in calcite sandstones may be of volcanic origins. We believe the high concentrations of chromium in the sandstones of the Istrian flysch basin and in the serpentinites and eclogites in Pohorje are geogenic in origin. Based on the mineral carriers of Cr we believe it is Cr3+ which is not toxic.