Fossils of the Fezouata Formation, which are usually squashed flat (although some do retain some degree of their original three-dimensionality) are often coated with a dusting of pyrite, and tin; this aspect of the fossil preservation is very similar to that at Chengjiang.[1] Non-mineralized appendages are often preserved.[6] While the formation as a whole is over 1,000 metres (3,300 ft) thick, only two intervals, 25 metres (82 ft) and 15 metres (49 ft) thick, provide exceptional preservation.[14][15] Both of these intervals are located near the top of the lower formation, corresponding to the Araneograptus murrayi and Hunnegraptus copiosus graptolite zones respectively.[4]