From the Swedish gyttja.

Lake-swamp or lagoonal silt deposits of organic origin containing large amounts of plankton and benthos remains with an admixture of minerals. Hittia is characterized by an increased concentration of iron oxides. It is developed in eutrophic water bodies.

A distinction is made between sapropel and saprocoll. Drying out, gyttja turns into a gelatinous mass, saprocoll, which is a valuable mineral fertilizer. Sapropel is the muddy sediments of fresh continental reservoirs, which contain more than 15% (by weight) of organic matter.

Classification:

Clay gyttja

Small-detrital gyttja

Large-detrital gyttja