Hematite and goethite in Telychian marine red beds of the east Baltic

Hematite and goethite were determined by X-ray diffractometry using natural goethite and hematite for calibration. The subtraction of diffractograms before and after ignition at 500[ddot]C was applied for goethite identification and quantification, and ZnO was used as internal standard for the matrix correction. Red terrigenous claystones from deep shelf facies revealed co-occurrences of hematite and goethite, on average 1.7% hematite and 0.6% goethite. Grey claystones from the onshore facies of deep shelf contained yellow goethitic layers with the goethite content from 1.6 to 12.5%. Red metabentonites, layers of altered volcanic ash, contained only hematite, on average 2.7%, and did not reveal goethite above the detection limit. The occurrence of red metabentonites points to the early diagenetic origin of hematite in volcanic ash beds as well as in red terrigenous host rock. Several pathways of hematite and goethite formation are considered for different rock types.