Goethite
Current inventory:  0 gems
 

  
Goethite was named in 1806 by Johann Georg Lenz to honor the German poet, novelist, playwrighter, philosopher and geoscientist Johann Wolfgang von Goethe (1749-1832).

Discovered in 1806; IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

α-Fe³⁺O(OH)

Iron Oxyhydroxide (with ferric iron)

Molecular Weight:

88.85 gm

Composition:

Iron

62.85 %

Fe

89.86 %

Fe₂O₃

Hydrogen

1.13 %

H

10.14 %

H₂O

Oxygen

36.01 %

O

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

Oxides

Strunz 8th Ed. ID:

4/F.06-30

Nickel-Strunz 10th Ed. ID:

4.FD.10

4 : OXIDES (Hydroxides, V[5,6] vanadates, arsenites, antimonites, bismuthites, sulfites, selenites, tellurites, iodates)
F : Hydroxides (without V or U)
D : Hydroxides with OH, without H₂O; chains of edge-sharing octahedra

Related to:

Diaspore Group. Trimorphous with Feroxyhyte and Lepidocrocite.

Members of Group:

Diaspore Group: Bracewellite, Diaspore, Goethite, Groutite, Montroseite, Tsumgallite

Varieties:

Alumogoethite, Ehrenwerthite

Synonyms:

Acicular iron ore, Allcharite, α-Goethite, Chileit (of Breithaupt), Ehrenwerthite (of Cornu), Fullonite, Götheite, Göthite, Hydrohematite, ICSD 28247, Limonite, Mesabite, needle ironstone, PDF 29-713, Przibramite (of Glocker), Yanthosiderite

Crystal Data

Crystallography:

Orthorhombic - Dipyramidal

Crystal Habit:

As prismatic crystals, striated || [001], to 45 cm, or tabular on {010}. More commonly as aggregates of capillary to acicular crystals, in divergent sprays, or reniform, botryoidal, or stalactitic masses with concentric or radial fibrous internal structure; nearly cryptocrystalline in “limonite”.

Twinning:

None

Physical Properties

Cleavage:

Perfect on {010}; less perfect on {100}

Fracture:

Irregular/Uneven

Tenacity:

Brittle

Moh's Hardness:

5.0 - 5.5; VHN = 667 (100 g load)

Density:

4.27 - 4.29 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Optical Properties

Color:

Blackish Brown; Yellowish to Reddish Brown in massive aggregates, may be banded; shades of Yellow in thin section; Gray with Bluish tint in reflected light, with Yellow, Red, Brown internal reflections

Transparency:

Opaque, Transparent on thin edges

Luster:

Imperfect adamantine, metallic to dull earthy; silky when fibrous

Refractive Index:

2.260 - 2.515  Biaxial ( - ); Uniaxial (–) for red light

Birefringence:

0.133 - 0.134

Dispersion:

Extreme; r > v

Pleochroism:

Strong; X = yellow to colorless; Y = yellow-brown, reddish orange; Z = yellow-orange, deep reddish orange

Anisotrophism:

Distinct in bluish grays. Gray with bluish tint with yellow, red, brown internal reflections.

Occurances

Geological Setting:

A common weathering product derived from numerous iron-bearing minerals in oxygenated environments; an important component of ore in weathered iron deposits. Also a primary precipitate in hydrothermal, marine, and bog environments upon oxidation of reduced iron-bearing waters.

Common Associations:

Lepidocrocite, Hematite, Pyrite, Siderite, Pyrolusite, Manganite, many other iron and manganese-bearing species.

Common Impurities:

Mn

Type Locality:

Hollertszug Mine, Herdorf, Siegerland, Rhineland-Palatinate, Germany

Year Discovered:

1806

View mineral photos:

Goethite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Goethite is a common mineral and is a popular species for mineral collectors but is rarely thought of in the gem trade. Goethite has, in the past, had a reputation of being a rather uninteresting, dull, black mineral. However, Goethite commonly creates a very nice dark backdrop matrix for vividly colored minerals such as Vanadinite. There are also beautiful massive specimens that show rainbows of irridescent colors. These irridescent specimens can be cut into "cabochons" or what I call "specigems". An example of this type of gem is pictured at the top of this page.

Sources for Goethite are widespread; some localities for good crystals include: from Siegen, North Rhine-Westphalia, and near Giessen, Hesse, Germany. At Príbram, Czech Republic. Exceptional crystals from the Restormel mine, Lanlivery; the Botallack mine, St. Just; and elsewhere in Cornwall, England. From Chaillac, Indre-et-Loire, France. In the USA, from the Pikes Peak district and Florissant, El Paso County, Colorado; an ore mineral in the Lake Superior district, as at the Jackson mine, Negaunee, and the Superior mine, Marquette, Marquette County, Michigan.
 

  
Goethite gems for sale:

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