Goethite is a brown hydroxide mineral, iron oxyhydroxide,
of composition FeO(OH). It is a major iron ore of
widespread occurrence, formed in bogs or by weathering of other iron minerals.
Goethite is very similar to limonite, but
is crystalline in the orthorhombic system as slender plates and velvety
needles. X-ray diffraction analysis
has shown that much supposed limonite is in fact goethite. Hardness: 5–5.5;
relative density: 3.3–4.3.
Mineral Information Institute
AND PLANETARY SCIENCE