1. mud: soft, wet earth.
  2. clay: (particles of less than 0.002mm); stiff, sticky earth that becomes hard when baked.
  3. silt: (particles of 0.002- 0.0625mm); when dried on hand will rub off easily.
  4. sand: (particles of 0.0625- 2.0mm); tiny grains of crushed or worn rock.
  5. stone: a general term for rock fragments ranging in size from pebbles and gravel to boulders or a large rock mass. (IHO Dictionary, S-32, 5th Edition, 5059)
  6. gravel: (particles of 2.0-4.0mm); small stones with coarse sand.
  7. pebbles: (particles of 4.0- 64.0mm); small stones made smooth and round by being rolled in water.
  8. cobbles: (particles of 64.0- 256.0mm); stones worn round and smooth by water and used for paving.
  9. rock: any formation of natural origin that constitutes an integral part of the lithosphere. The natural occurring material that forms firm, hard, and solid masses. (adapted from IHO Dictionary, S-32, 5th Edition, 4415)
  10. lava: the fluid or semi-fluid matter flowing from a volcano. The substance that results from the cooling of the molten rock. Part of the ocean bed is composed of lava. (IHO Dictionary, S-32, 5th Edition, 2680)
  11. coral: hard calcareous skeletons of many tribes of marine polyps. (IHO Dictionary, S-32, 5th Edition, 1061)
  12. shells: exoskeletons of various water dwelling animals. (adapted from IHO Dictionary, S-32, 5th Edition, 4680)
  13. boulder: a rounded rock with diameter of 256 mm or larger. (adapted from IHO Dictionary, S-32, 5th Edition, 527)