1 (biostratigraphic zone) A unit of rock characterized by a clearly defined fossil content. To avoid confusion with other types of zone the term ‘biozone’ (short for ‘biostratigraphic zone’) is preferred by many authorities, although the term ‘biozone’ is also used in a different sense. The term is usually qualified to denote the type of zone. See acme zone; assemblage zone; concurrent range zone; lineage zone; oppel zone; range zone; subzone; taxon range zone; teilzone; zonule; and index fossil.
2 In crystallography, a set of crystal faces whose intersecting edges are parallel. They are also parallel to, and may be rotated about, a zone axis. See crystal zoning.
3 See metamorphic zone.