Polarised light micrograph of Middle Bunter sandstone from a boulder field in Welzberg by Calw, Black Forest, Germany. Bunter sandstone mainly consists of sandstone layers of the Lower Triassic series. It is one of three characteristic Triassic units, together with the Muschelkalk and Keuper that form the Germanic Trias Supergroup. Bunter sandstone is similar in age, facies and lithology to the Bunter of the British Isles. It normally lies above Permian Zechstein and below Muschelkalk. It formed between 251 and 243 million years ago. Magnification: x4 when printed at 15 centimetres wide.