Picromerite

Picromerite (synonyms: schoenite, schönite) is a mineral from the class of hydrous sulfates lacking additional anions, and containing medium to large cations according to the Nickel–Strunz classification.[3]

Picromerite
Picromerite on halite
General
CategorySulfate mineral
Formula
(repeating unit)		K2Mg(SO4)2·6H2O
IMA symbolPmr[1]
Strunz classification7.CC.60
Dana classification29.03.06.01
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupP21/a
Unit cella = 9.07, b = 12.21,
c = 6.11 [Å]; β = 104,8°; Z = 2
Identification
ColorColorless; white, grey, reddish, yellowish
Crystal habitmassive aggregates; crusts; prismatic crystals
Cleavageperfect {201}[2]
Mohs scale hardness2.5
LusterVitreous
StreakWhite
DiaphaneityTransparent
Density2.03[2]
Optical propertiesBiaxial (+)
Refractive indexnα = 1.461 nβ = 1.463 nγ = 1.476[3]
Birefringenceδ = 0.015[3]
2V angleMeasured: 47°[3]
Solubilityin cold water
Tastebitter
References[3][2][4]

Etymology

The name comes from the Greek words πικρός [pikros] for "bitter" and μέρος [meros] for "part", and relates to the bitter taste of the mineral.

Occurrence

Picromerite is found on comparatively few places, currently (2015) only about 40 localities are known.[3] It was first identified in active volcanic fumaroles on Mount Vesuvius by Arcangelo Scacchi in 1855[5] and has also been found in volcanic deposits on Mount Etna and on Hawai'i.

It is more commonly found in the kainite zones of some marine salt deposits, among them salt mines in Thuringia, Lower Saxony and Saxony-Anhalt (Germany), near Hall in Tirol, Hallstatt and Bad Ischl (Austria), near Whitby (UK), and in the Carlsbad Potash District (New Mexico), also on salt lakes in western China.

Picromerite can also form in sulfate-rich hydrothermal ore deposits and is found in slag heaps of some ore and coal mines.

Picromerite is often accompanied by anhydrite, epsomite, halite, hohmannite, kainite, metasideronatrite and metavoltine, depending on the locality.

Properties

Picromerite dehydrates in dry air, and crystals then show dull, spherical dehydration zones. Progressive dehydration leads to leonite.

References
  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. Picromerite, In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Hrsg.): Handbook of Mineralogy, Mineralogical Society of America. 2001 (PDF 66,3 kB).
  3. "Picromerite". Mindat.
  4. "Picromerite". Webmineral.com.
  5. Arcangelo Scacchi: Memoria sullo incendio vesuviano del mese di Maggio. Nobile, Napoli 1855, p. 191.
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