Basement rocks of Santorini have been locally impregnated by iron oxides and other minerals. The hydrothermal fluids which caused the mineralization have extensively altered the impregnated rocks, but left granditic garnets in these unaffected.

Mössbauer spectroscopy and differential X-ray diffraction show that the iron oxides present are goethite and hematite in a ratio of about 2 : 1. The presence of hematite indicates that these minerals formed, directly from a hydrothermal phase, at higher temperatures than the recent submarine iron oxide deposits of Santorini, which contain no hematite.