Goethite is hydrated iron oxide[?], FeO(OH). Its hardness ranges from 5.0 to 5.5, and its specific gravity varies from 3.3 to 4.3. It is not generally considered very interesting as a mineral specimen; its main use is as an ironore.
... See the TCPA / Pallidium FAQ maintained by Professor Ross J Anderson on his Web site at www.cl.cam.ac.uk/~rja14/tcpa-faq.html/ for a clear discussion of two prominent ...