Museums Victoria
Museum Victoria: Pseudofossils: Concretions and Dendrites
Pseudofossils are materials that are sometimes mistaken for fossils. They include concretions and dendrites, described here.
ArtLex
Art Lex: Shape
This online dictionary of art from Artlex provides terms is a valuable tool. Shape is on the Sg-Sh page. Just scroll down to Shape and read a definition with links to other important terms.