How to identify a fossil

Location narrows the possibilities enormously. A spiral from a Dorset beach is almost certainly an ammonite; a glossy triangle from Bracklesham is almost certainly a shark tooth; a ribbed shell from Carboniferous limestone in Northumberland is almost certainly a brachiopod.

Record the site before you do anything else. A fossil without provenance loses most of its scientific and much of its personal value.

• Is it symmetrical, and across which axis? Brachiopods are symmetrical across each shell; bivalves between their two shells.
• Does it coil? Flat coil means ammonite; a coil rising into a cone means gastropod.
• Does it repeat? Segments suggest trilobites; ribs suggest ammonites or shells; a five-part pattern means an echinoderm.
• Is it heavy, and what does a broken surface show? Honeycomb means bone; radiating crystals mean belemnite.

The rock the fossil sits in tells you its age, and age rules candidates in or out. Trilobites cannot occur in Jurassic shale; ammonites cannot occur in Carboniferous limestone. If you know the formation, you have halved the problem.

Museums and heritage centres identify finds routinely and without charge — Charmouth Heritage Coast Centre, Lyme Regis Museum, Dinosaur Isle on the Isle of Wight and the Norfolk Museums Service all do. Take a clear photograph with a scale, and be able to say where and when you found it.