The iron ore of the Grundhamn mine on one of the Ulvö islands in the Ångermanland archipelago in northern Sweden is to be regarded as a highly ferriferous variety of a post-Jotnian dolerite. Some peculiarities in the chemical composition of different concentrates from samples of the ore could not be explained otherwise than by supposing that the most common mineral of the ore was a substance, that not earlier had been discovered in Nature. By means of microscopic studies, chemical analysis and X-ray examinations it was found, that the unknown mineral was a ferro-orthotitanate, the spinel Fe2TiO4. In the ore the ferro-ortho-titanate appears in a blend of various spinels, magnetite being the second most frequent one.