99% rock and 1 % sand, silt and organic debris. The rocks are 75% igneous and 25% metamorphic. A good many of the rocks classified as igneous could be classified as low grade gneisses
Cite the IMLGS database as: Curators of Marine and Lacustrine Geological Samples Consortium. The Index to Marine and Lacustrine Geological Samples (IMLGS). National Geophysical Data Center, NOAA. doi:10.7289/V5H41PB8 [date of access].