Diatoms - Overview

Diatoms are single-celled or colonial microalgae found in almost all freshwater and marine habitats. Diatoms are characterized by having a two-part cell wall composed of biogenic opaline silica. The remains of diatoms are often one of the main inorganic components seen in smear slides and can account for over 80% of dry sediment weight (more commonly 2-10%). Each part of a diatom cell wall is called a valve, and the shape, ornamentation, and patterns on the diatom valve can be used to identify each of the over 25,000 living species.

In addition to noting the presence or absence of diatoms in smear slides, other simple qualitative and quantitative measures can be made from smear slides related to abundance, preservation, and diatom ecology. For identification of diatoms to the genus- or species-level, visit Diatoms of the United States.