earthstory: Agatised coral Silica replaces all sorts of…
Agatised coral
Silica replaces all sorts of things, usually after the remains of living creatures have entered the geological record in a layer of deposited sediments. Obvious examples include opalised shells (see http://tinyurl.com/okb7k2z), petrified wood ( see http://tinyurl.com/me4be8t) and dinosaur bone (see http://tinyurl.com/qfr779b).