The matrix of turbidites, which are sediment deposits from underwater currents, can give clues about the density of these currents. Experiments in a circular flume show that the amount of fine particles in the matrix depends on the ratio of fine particles to water, not just the ratio of sand to fine particles. Coarser deep-sea sands have about 1-2% fine particles, indicating turbidity currents with 5-10% fine particles. The density of these currents can vary, but is generally around 1.1-1.2. Coarse turbidites usually have less than 10% fine particles, while fine-grained ones can have up to 20%. This suggests that marine graywackes with a high matrix content were weakly metamorphic turbidites. The experimental deposits show good sorting, similar to natural turbidites, and grain-size analyses often show a bend in fine sand or silt sizes.