Mineral Information and Data:

Jarosite
KFe3+3(SO4)2(OH)6 [CNMNC approved formula]

Named for the locality - Barranco del Jaroso, Spain, from where the first scientifically studied specimens were obtained. First published in 1852. Redfined per nomenclature of alunite supergroup (IMA, 1999).

IMA status : Redefined IMA Approved; 1999 ()
CLASSIFICATION 
Dana
(8th edition) :
30.02.05.01  
  (30) Anhydrous Sulfates Containing Hydroxyl or Halogen
  (30.02) where (A B)2 XO4 Zq
  (30.02.05) Alunite Group (Jarosite Subgroup)
  
Nickel-Strunz
(10th edition) :
07.BC.10
  (07) Sulfates (selenates, tellurates, chromates, molybdates, wolframates)
  (07.B) Sulfates (selenates, etc.) with Additional Anions, without H2O
  (07.BC) With medium-sized and large cations
  
Crystal system: Trigonal System
Point group (H-M): 3m (or 3 2/m) — hexagonal-scalenohedral
Space group: R3m
Unit cell: a = 7.29 Å, c = 17.16 Å, Z=3
Crystal Habit: As well-formed crystals, pseudocubic rhombohedral {0112} or tabular on {0001}, to 25 cm; typically as minutely crystalline crusts, also fibrous, nodular, granular, pulverulent, earthy.
  
Color: Amber-yellow to dark brown
Diaphaneity: Transparent to translucent
Luster: Subadamantine to vitreous, resinous on fractures
Hardness (Mohs): 2.5 - 3.5
Measured Density: 2.91 – 3.26 g/cm3
Cleavage: On {0001}, distinct
Tenacity: Brittle
Fracture: Uneven to conchoidal
Streak: Pale yellow
  
Polymorphism and Series: Forms a series with natrojarosite
Geologic Setting: A secondary mineral in oxidized portions of sulfide-bearing rocks, typically altering from pyrite; less common as a low-temperature, primary hydrothermal mineral, including as deposits around hot springs.
Mineral Association: Alunite, pyrite
  
Other Properties: Pyroelectric. BioMineral.

 

Jarosite
Origin: Lovelock, Pershing Co., Nevada, U.S.A.
Sample size: Microscopic image
Photo and Owner: Lou Perloff

 

Jarosite
Origin: Lovelock, Pershing Co., Nevada, U.S.A.
Sample size: Microscopic image
Photo and Owner: Lou Perloff

 

Jarosite
Origin: Soureza, Attika, Greece
Sample size: 2 x 2 x 1.5 cm
Photo: Tom Loomis

 

Jarosite
(zoom-in of above)

 

Jarosite
Origin: Post Pit, Carlin Trend, Eureka County, Nevada, U.S.A.
Sample size: 3.5 x 3 x 2.5 cm
Photo: Dan Weinrich

 

Jarosite
(zoom-in of above)

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