The Mineral GOETHITE

Chemical Formula: FeO(OH), Hydrated Iron Oxide
Class: Oxides and Hydroxides
Group: Goethite
Uses: important ore of iron, pigment
Specimens

Goethite has had a reputation for making rather uninteresting, dull and "dirty" mineral specimens. This is definitely not true of many of the fine specimens available to collectors today. Some good pieces show splendid radiating clusters of deep black crystals. Massive stalactitic forms show rainbows of irridescent colors on surreal landscapes. Many times Goethite forms the backdrop or matrix for other minerals such as red Vanadinite, making a visually appealing mineral specimen.

PHYSICAL CHARACTERISTICS:

Color is yellow, brown, brownish red to black. Sometimes tarnished with irridescent colors.
Luster is earthy to dull for massive forms and metallic for crystals.
Transparency crystals are opaque.
Crystal System is orthorhombic; 2/m 2/m 2/m
Crystal Habits include prismatic and platy crystals, massive and aggregate forms include internally radiating or fibrous; reniform, botryoidal and stalactitic.
Cleavage is perfect in one direction.
Fracture is uneven to splintery.
Hardness is 5-5.5
Specific Gravity is variable at 3.3 to 4.3 (light for metallic minerals)
Streak is brown, brownish yellow to orange yellow.
Associated Minerals include a large list of minerals (particularly secondary deposit minerals).
Notable Occurences include many iron mines around the world; especially nice specimens come from England, Mexico, and the Lake Superior region in Michigan, USA.
Best Field Indicators are crystal habit, streak and tarnish.