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John Pickering
MgAl2(SO4)4 · 22H2O
Colourless to white, ...
1½ - 2
For John Pickering (February 7, 1777 Salem - May 5, 1846 Boston), American linguist and philologist.
Halotrichite Group; Halotrichite-Pickeringite Series.
The Mg analogue of Halotrichite.

At least a partial series entends toward Apjohnite.

Classification of Pickeringite

Approved, 'Grandfathered' (first described prior to 1959)

7 : SULFATES (selenates, tellurates, chromates, molybdates, wolframates)
C : Sulfates (selenates, etc.) without additional anions, with H2O
B : With only medium-sized cations

7 : AB2(XO4)4·H2O

25 : Sulphates
3 : Sulphates of Mg

Physical Properties of Pickeringite

Diaphaneity (Transparency):
Colourless to white, light yellow, pale pink, gray; colourless in transmitted light
Hardness (Mohs):
1½ - 2
On {010} poor.
1.73 - 1.79 g/cm3 (Measured)    1.84 g/cm3 (Calculated)
Pure end-member values.

Optical Data of Pickeringite

Biaxial (-)
RI values:
nα = 1.475 nβ = 1.480 nγ = 1.483
Measured: 60° , Calculated: 80°
Max Birefringence:
δ = 0.008
Image shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:

Chemical Properties of Pickeringite

MgAl2(SO4)4 · 22H2O
Elements listed in formula:
Analytical Data:
Completely soluble in water to an acid solution.
Common Impurities:

Crystallography of Pickeringite

Crystal System:
Class (H-M):
2/m - Prismatic
Space Group:
Space Group Setting:
Cell Parameters:
a = 20.8Å, b = 24.2Å, c = 6.18Å
β = 95°
a:b:c = 0.86 : 1 : 0.255
Unit Cell Volume:
V 3,098.93 ų (Calculated from Unit Cell)
Crystals acicular [001]; distinctly terminated crystals rare. Radial or matted aggregates of hair-like crystals; tufted; spheroidal; as incrustations or effloresences; asbestiform. Larger crystals may be hollow or contain bubbles of liquid or gas.
X-Ray Powder Diffraction:
Image Loading

Radiation - Copper Kα
Data Set:
Data courtesy of RRUFF project at University of Arizona, used with permission.
X-Ray Powder Diffraction Data:
6.08 (20)
4.97 (20)
4.82 (100)
4.32 (35)
4.122 (30)
3.510 (90)
3.791 (30)
ICDD 12-299.

Occurrences of Pickeringite

Type Occurrence of Pickeringite

Relationship of Pickeringite to other Species

Forms a series with Halotrichite (see here)
Other Members of Group:
ApjohniteMn2+Al2(SO4)4 · 22H2O
BíliniteFe2+Fe23+(SO4)4 · 22H2O
Dietrichite(Zn,Fe2+,Mn2+)Al2(SO4)4 · 22H2O
HalotrichiteFeAl2(SO4)4 · 22H2O
7.CB.05DwornikiteNiSO4 · H2O
7.CB.05GunningiteZnSO4 · H2O
7.CB.05KieseriteMgSO4 · H2O
7.CB.05PoiteviniteCuSO4 · H2O
7.CB.05SzmikiteMn2+SO4 · H2O
7.CB.05SzomolnokiteFe2+SO4 · H2O
7.CB.05CobaltkieseriteCoSO4 · H2O
7.CB.07SanderiteMgSO4 · 2H2O
7.CB.10BonattiteCuSO4 · 3H2O
7.CB.15AplowiteCoSO4 · 4H2O
7.CB.15BoyleiteZnSO4 · 4H2O
7.CB.15IlesiteMn2+SO4 · 4H2O
7.CB.15RozeniteFe2+SO4 · 4H2O
7.CB.15StarkeyiteMgSO4 · 4H2O
7.CB.15DrobeciteCdSO4 · 4H2O
7.CB.15CranswickiteMgSO4 · 4H2O
7.CB.20ChalcanthiteCuSO4 · 5H2O
7.CB.20JôkokuiteMn2+SO4 · 5H2O
7.CB.20PentahydriteMgSO4 · 5H2O
7.CB.20Siderotil(Fe,Cu)SO4 · 5H2O
7.CB.25BianchiteZnSO4 · 6H2O
7.CB.25ChvaleticeiteMnSO4 · 6H2O
7.CB.25FerrohexahydriteFe2+SO4 · 6H2O
7.CB.25HexahydriteMgSO4 · 6H2O
7.CB.25MoorhouseiteCoSO4 · 6H2O
7.CB.25NickelhexahydriteNiSO4 · 6H2O
7.CB.30RetgersiteNiSO4 · 6H2O
7.CB.35BieberiteCoSO4 · 7H2O
7.CB.35BoothiteCuSO4 · 7H2O
7.CB.35MallarditeMn 2+SO4 · 7H2O
7.CB.35MelanteriteFe2+SO4 · 7H2O
7.CB.35ZincmelanteriteZnSO4 · 7H2O
7.CB.35Alpersite(Mg,Cu2+)SO4 · 7H2O
7.CB.40EpsomiteMgSO4 · 7H2O
7.CB.40GoslariteZnSO4 · 7H2O
7.CB.40MorenositeNiSO4 · 7H2O
7.CB.45AlunogenAl2(SO4)3(H2O)12 · 5H2O
7.CB.45Meta-alunogenAl2(SO4)3 · 14H2O
7.CB.50AluminocoquimbiteAlFe(SO4)3 · 9H2O
7.CB.55CoquimbiteFe23+(SO4)3 · 9H2O
7.CB.55ParacoquimbiteFe23+(SO4)3 · 9H2O
7.CB.55Rhomboclase(H3O)Fe3+(SO4)2 · 3H2O
7.CB.60KorneliteFe23+(SO4)3 · 7H2O
7.CB.65QuenstedtiteFe23+(SO4)3 · 11H2O
7.CB.70LauseniteFe23+(SO4)3 · 5H2O
7.CB.75LishizheniteZnFe23+(SO4)4 · 14H2O
7.CB.75RömeriteFe2+Fe23+(SO4)4 · 14H2O
7.CB.80RansomiteCuFe23+(SO4)4 · 6H2O
7.CB.85ApjohniteMn2+Al2(SO4)4 · 22H2O
7.CB.85BíliniteFe2+Fe23+(SO4)4 · 22H2O
7.CB.85DietrichiteZnAl2(SO4)4 · 22H2O
7.CB.85HalotrichiteFe2+Al2(SO4)4 · 22H2O
7.CB.85RedingtoniteFe2+Cr2(SO4)4 · 22H2O
7.CB.85WupatkiiteCoAl2(SO4)4 · 22H2O
7.CB.90MeridianiiteMgSO4 · 11H2O
25.3.1KieseriteMgSO4 · H2O
25.3.2SanderiteMgSO4 · 2H2O
25.3.3StarkeyiteMgSO4 · 4H2O
25.3.4PentahydriteMgSO4 · 5H2O
25.3.5HexahydriteMgSO4 · 6H2O
25.3.6EpsomiteMgSO4 · 7H2O
25.3.7CaminiteMg7(SO4)5(OH)4 · H2O
25.3.9BlöditeNa2Mg(SO4)2 · 4H2O
25.3.10KonyaiteNa2Mg(SO4)2 · 5H2O
25.3.11LöweiteNa12Mg7(SO4)13 · 15H2O
25.3.12UklonskoviteNaMgSO4(OH) · 2H2O
25.3.14LeoniteK2Mg(SO4)2 · 4H2O
25.3.15PicromeriteK2Mg(SO4)2 · 6H2O
25.3.17Boussingaultite(NH4)2Mg(SO4)2 · 6H2O

Other Names for Pickeringite

Other Information

Other Information:
Soluble in H2O, astringent taste.
Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

References for Pickeringite

Reference List:
Hayes A A (1844) Description and analysis of pickeringite, a native magnesian alum. American Journal of Science and Arts 46, 360-362

Dana, J.D. (1868) System of Mineralogy, 5th. Edition, New York: 654 (as Bosjemanite).

Roster (1876) Boll. com. geol. Ital.: 302 (as Picroallumogene).

Goldsmith, E. (1877), On sonomaite: Acad. Nat. Sci. Philadelphia Proc.: 28: 263-264.

Doelter (1882) Vulk. Gesteine und Min. der Capverde Inseln: 93 (as Dumreicherit).

Darapsky (1887) Neues Jahrbuch für Mineralogie, Geologie und Paleontologie, Heidelberg, Stuttgart: I: 131 (as Sesqui-Magnesia-alaun).

Darapsky (1890) Neues Jahrbuch für Mineralogie, Geologie und Paleontologie, Heidelberg, Stuttgart: I: 49 (as Aromite).

Uhlig (1912) Centralblatt für Mineralogie, Geologie und Paleontologie, Stuttgart: 723.

Zsivy (1920) Zeitschrift für Kristallographie, Mineralogie und Petrographie, Leipzig: 55: 629.

Larsen, E.S. (1921) The Microscopic Determination of the Nonopaque Minerals, First edition, USGS Bulletin 679: 41.

Schairer and Lawson (1926) American Journal of Science: 11: 301.

Doelter, C. (1927) Handbuch der Mineral-chemie: 4 [2]: 523, 545.

Vavrinecz (1929) Magyar Chemiai Folyóirat, Budapest: 35: 1.

Hintze, Carl (1930) Handbuch der Mineralogie. Berlin and Leipzig. 6 volumes: 1 [3B]: 4505, 4512.

Kokta (1930) Přiroda, Brno: 32: 381.

Rutherford (1932) American Mineralogist: 17: 401.

Tokody (1933) Földtani Közlöny, Budapest (Magyarhone Földtani Torsulat): 62: 187.

Meixner and Pillewizer (1937) Zbl. Min.: 263.

Bandy (1938) American Mineralogist: 23: 724.

Gordon S G (1942) Results of the Chilean mineralogical expedition of 1938. Part VII.—The crystallography of alunogen, meta-alunogen and pickeringite. Notulae Naturae of The Academy of Natural Sciences of Philadelphia 101, 1-9

Palache, C., Berman, H., & Frondel, C. (1951), The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana, Yale University 1837-1892, Volume II. John Wiley and Sons, Inc., New York, 7th edition, revised and enlarged, 1124 pp.: 523-527.

Quartieri S, Triscari M, Viani A (2000) Crystal structure of the hydrated sulphate pickeringite (MgAl2(SO4)4·22H2O): X-ray powder diffraction study. European Journal of Mineralogy 12, 1131-1138

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Localities for Pickeringite

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