The Mineral goethite

Goethite is a common mineral, and is a frequent matrix material for other more aesthetic minerals. It is usually a dark, uninteresting mineral, though specimens from a handful of locations (especially Colorado) are remarkable for their delicate and beautiful crystal growths and velvety botryoidal growths. Goethite is also frequent as black crystal sprays that form within geodes on drusy Quartz. It commonly forms a pseudomorph after other minerals, especially Marcasite, Pyrite, Siderite, and Gypsum.

Chemical Formula

FeO(OH)

Color

Black, brown, yellowish-brown, reddish-brown, yellow. May be iridescent with a multicolored rainbow-like display of darker toned colors. Rarely banded.

Crystal System

Orthorhombic

Properties

Streak Brownish-yellow to yellow

Hardness 5 - 5.5

Transparency Opaque

Specific Gravity 3.3 - 4.3

Luster Submetallic, silky, dull

Cleavage 1,1

Fracture Splintery, uneven

Tenacity Brittle

Other ID Marks Will become attracted to magnetic fields upon heating.

Crystal Habits

Individual crystals are in small, flattened blades and plates, or finely acicular with a velvety appearance. Most often in botryoidal, reniform, or stalactitic aggregates of radiating crystals or ball-like crystals. Also grainy, in veins, concretionary, oolitic, and in earthy masses. Goethite often assumes the shape of other minerals forming a pseudomorph in place of the original mineral or as a coating above it.

3D Crystal Atlas

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Additional Information

Composition Iron hydroxide, often with some manganese

In Group Oxides; Hydroxides

Striking Features Streak, color, and crystal aggregate formations

Environment As a secondary mineral in hydrothermal replacement deposits, in igneous pegmatites and basalt, and in sandstones, limestones, and clays.

Rock Type Igneous, Sedimentary

Other Names

	Bog Iron	Synonym used for both Goethite and Limonite.
	Bog Iron Ore	Synonym used for both Goethite and Limonite.
	Brown Iron Ore	Synonym used for both Goethite and Limonite.
	Wood Iron	Synonym used for both Goethite and Limonite.

Varieties

Turgite

 -   Iridescent Goethite mixed with Hematite.

Uses

Goethite is used as an ore of iron.

Noteworthy Localities

Goethite is found throughout the world, though collection-worthy specimens are less common. Branching stalactites and botryoidal masses, often associated with bright contrasting Vanadinite, come from the Four Man Mine, Taouz, Morocco. Recent finds of branching Goethite pseudomorphs after Marcasite are exceptional at the Farfara Oasis, in the White Desert of Egypt. Rainbow-like iridescent Goethite coating sandstone was found in the Munday's Hill Quarry, Leighton Buzzard, England; and highly iridescent growths come from Tharsis, Alosno, Spain. Sharp bladed crystals come from Chaillac, Indre, France.

Fascinating, elongated pseudomorphs of Goethite after Gypsum were found in Santa Eulalia, Chihuahua, Mexico; and rounded Goethite balls have come from Wawa, Ontario, Canada.

In the U.S., exceptionally pretty acicular Goethite crystals with a sharp luster are found at the Crystal Peak and Lake George areas, Park and Teller Cos., Colorado. Perfectly crystallized Goethite pseudomorphs after Pyrite come from Pelican Point, Utah Co., Utah; and attractive botryoidal forms were found in the famous Copper Queen Mine, Bisbee, Cochise Co., Arizona. Large deposits of Goethite can be found in Michigan in the Menominee iron range, Iron Co.; and in the Marquette iron range, Marquette Co. A highly iridescent Goethite is well-known from Graves Mountain, Lincoln Co., Georgia. Large botryoidal plates and clusters can be found in Oreland, Montgomery Co., Pennsylvania.

Common Mineral Associations

Quartz, Calcite, Pyrite, Hematite, Manganite, Psilomelane

Distingushing Similar Minerals

Hematite - Has a reddish-brown streak, heavier, and usually more metallic lustered.
Limonite - Lacks definitive crystal structure.

goethite Photos

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