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Botryoidal Goethite Blobs

The Mineral goethite




Goethite is a very common mineral, and is a frequent matrix material for other more aesthetic minerals. It is usually an ugly dark mineral, though specimens from a handful of locations (especially Colorado) are remarkable for their delicate and beautiful crystal growths or oddly formed botryoidal and stalactitic velvety 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. Goethite is named after Johann Wolfgang von Goethe (1749-1832), the famed German poet, philosopher, biologist, and mineral enthusiast.
Chemical Formula FeO(OH)
Composition Iron hydroxide, often with some manganese
Variable Formula (Fe,Mn)O(OH)
Color Black, brown, yellowish-brown, reddish-brown, yellow. May be iridescent with a multicolored rainbow-like display of darker toned colors. Rarely banded.
Streak Brownish-yellow to yellow
Hardness 5 - 5.5
Crystal System Orthorhombic
3D Crystal Atlas
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Crystal Forms
and Aggregates
Individual crystals are in small, flattened blades and plates, or finely acicular with a velvety look. 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.
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.
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 sedimentary sandstones, limestones, and clays.
Rock Type Igneous, Sedimentary
Popularity (1-4) 2
Prevalence (1-3) 1
Demand (1-3) 2

Goethite ON EBAY
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.

VARIETIES
 -  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 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

DISTINGUISHING 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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