Goethite

Goethite
General
Categoryoxide minerals hydroxide subgroup
Formula
(repeating unit)
α-FeO(OH)
IMA symbolGth[1]
Strunz classification4.FD.10
Crystal systemOrthorhombic
Crystal classDipyramidal (mmm)
H–M symbol: (2/m 2/m 2/m)
Space groupPbnm
Identification
ColorYellowish to reddish to dark brown or black
Crystal habitradial acicular, mammillary, botryoidal, stalactitic, massive, as encrustation, as pseudomorph; may be banded or iridescent
CleavagePerfect {010}
FractureUneven to splintery
Mohs scale hardness5.0–5.5
LusterAdamantine to dull
StreakBrown, brownish yellow to orange yellow
Specific gravity3.3–4.3
Refractive indexOpaque to sub-translucent
FusibilityFusible at 5–5.5
SolubilityHCl soluble
Other characteristicsweakly magnetic
References[2][3][4][5]
Unusual specimen of goethite replacing a gypsum stalactite; the center is hollow. From Santa Eulalia, Chihuahua, Mexico.

Goethite (/ˈɡɜːrtt/,[6][7] US also /ˈɡθt/[8][9]) is a mineral of the diaspore group, consisting of iron(III) oxide-hydroxide, specifically the α-polymorph. It is found in soil and other low-temperature environments such as sediment. Goethite has been well known since ancient times for its use as a pigment (brown ochre). Evidence has been found of its use in paint pigment samples taken from the caves of Lascaux in France. It was first described in 1806 based on samples found in the Hollertszug Mine in Herdorf, Germany.[4] The mineral was named after the German polymath and poet Johann Wolfgang von Goethe (1749–1832).

  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ Hurlbut, Cornelius S.; Klein, Cornelis (1985). Manual of Mineralogy (20th ed.). Wiley. ISBN 0-471-80580-7.
  3. ^ Barthelmy, David (2012). "Goethite Mineral Data". Mineralogy Database. Retrieved 8 April 2022.
  4. ^ a b Goethite, Mindat.org
  5. ^ Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C. (2005). "Goethite" (PDF). Handbook of Mineralogy. Mineral Data Publishing. Archived (PDF) from the original on 2022-10-09. Retrieved 14 March 2022.
  6. ^ "goethite". Lexico UK English Dictionary. Oxford University Press. Archived from the original on August 5, 2021.
  7. ^ "goethite". Merriam-Webster.com Dictionary.
  8. ^ "goethite". Dictionary.com Unabridged (Online). n.d.
  9. ^ "goethite". The American Heritage Dictionary of the English Language (5th ed.). HarperCollins.

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