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Limonite  (variety of Goethite)
Current inventory:  0 gems
 

 
Limonite is named from the Greek for meadow, from occurrences in bogs. Goethite is named for German poet, novelist, playwrighter, philosopher and geoscientist Johann Wolfgang von Goethe (1749-1832).

Discovered in 1806 (Goethite);   IMA status: Limonite is Not Valid

Chemistry

Chemical Formula:

FeO(OH) · nH20

Hydrated Iron Oxide

Formula Notes:

While a "generic" formula is often given as stated above, "Limonite" is really quite variable in composition - both in its levels of hydration and hydroxylation and in its cationic content. There really is no formual for it.

Molecular Weight:

88.85 gm (Geothite)

Composition (Goethite): 

Classification

Mineral Classification:

Oxides

Strunz 8th Ed. ID:

4/F.06-30 (Geothite)

Nickel-Strunz 10th Ed. ID:

4.FD.10 (Geothite)

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 (Goethite)

Varieties:

Adlerstein, Alumolimonite, Auriferous Limonite, Avasite, Bean Ore, Chromiferous Limonite, Liminitogelite, Limnite, Stilpnosiderite

Synonyms:

Bog Ore, Brown Hematite, Brown Ocher, Brown Umber, Eisenoxyd-Hydrat, Ferrite (of Vogelsang), Ferrohydrite, Ferrum limosum, Gel-Goethite, Hydroferrite, Hydrosiderite, Hyposiderite, Marsh Ore, Meadow Ore, Morasterz, Ortstein, Pecheisenstein, Perlimonite, Raseneisenstein, Seeerz, Sumpfertz, Umber, Xanthosiderite (of Schmid), Yellow Ochre

Crystal Data

Crystallography:

Orthorhombic - Dipyramidal (Goethite)

Crystal Habit:

While "limonite" is amorphous, a number of minerals are noted for decomposing to it without losing their crystal shape - particularly pyrite crystals. Any "crystals" of "limonite" are actually pseudomorphs of other minerals which have decomposed in this fashion. Limonite is typically massive and may be very soft.

Twinning:

None

Physical Properties

Cleavage:

None

Fracture:

Irregular/Uneven

Tenacity:

Brittle

Moh's Hardness:

4.0 - 5.5

Density:

2.70 - 4.30 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Optical Properties

Color:

Light Brown to Brown, may be Yellowish-Brown

Transparency:

Opaque

Luster:

Imperfect Adamantine Metallic to dull Earthy

Refractive Index:

R1–R2: (400) 17.5–19.2, (420) 16.7–18.3, (440) 15.9–17.4, (460) 15.2–16.7, (480) 14.6–16.0, (500) 14.1–15.5, (520) 13.7–15.0, (540) 13.3–14.6, (560) 13.0–14.3, (580) 12.8–14.0, (600) 12.5–13.7, (620) 12.4–13.5, (640) 12.2–13.4, (660) 12.0–13.2, (680) 12.0–13.1, (700) 11.9–13.0

Birefringence:

0.00 (Opaque)

Dispersion:

Extreme; r > v (Geothite)

Occurances

Geological Setting:

A very common material in the oxidized zones of iron-bearing deposits, it is produced by the decomposition of many iron minerals, particularly Pyrite, with water being retained in varying amounts.

Common Associations:

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

Type Locality:

n/a

Year Discovered:

1806 (Goethite)

View mineral photos:

Limonite Mineral Photos and Locations

More Information

Mindat.org (Limonite)

Mindat.org (Goethite)
Webmineral.com (Goethite)

"Limonite" is a generic term currently used for undifferentiated hydrated iron oxides - often hydrated Goethite, with no visible crystals, and a yellow-brown streak. Limonite is not an IMA approved mineral name. Although it is most commonly the mineral species Goethite, it can also consist of varying proportions of Maghemite, Hematite, Lepidocrocite, Hisingerite, Pitticite, and Jarosite Group species, etc.

While Limonite is amorphous, a number of minerals are noted for decomposing to it without losing their crystal shape - particularly Pyrite crystals. Any "crystals" of "Limonite" are actually pseudomorphs of other minerals which have decomposed in this fashion. Limonite is typically massive and may be very soft.

Limonite is a very common material in the oxidized zones of iron-bearing deposits and can be found at many locations worldwide.
 

  
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