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Hexahydrite

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Formula:
MgSO4 · 6H2O
System:
Monoclinic
Colour:
Colourless, white, pale ...
Lustre:
Sub-Vitreous, Pearly, Dull, Earthy
Hardness:
2 - 2½
Name:
Named in 1911 by Robert Angus Alister Johnston in allusion to its composition, having six (HEXA-) molecules of water (HYDR-) in its formula.
Hexahydrite Group. May dehydrate to starkeyite (Chou, 2005).


Classification of Hexahydrite

Approved, 'Grandfathered' (first described prior to 1959)
7.CB.25

7 : SULFATES (selenates, tellurates, chromates, molybdates, wolframates)
C : Sulfates (selenates, etc.) without additional anions, with H2O
B : With only medium-sized cations
29.6.8.1

29 : HYDRATED ACID AND NORMAL SULFATES
6 : AXO4·xH2O
25.3.5

25 : Sulphates
3 : Sulphates of Mg

Physical Properties of Hexahydrite

Sub-Vitreous, Pearly, Dull, Earthy
Diaphaneity (Transparency):
Transparent, Translucent
Colour:
Colourless, white, pale greenish white; colourless in transmitted light.
Streak:
White
Hardness (Mohs):
2 - 2½
Tenacity:
Brittle
Cleavage:
Perfect
On {100}, perfect.
Fracture:
Conchoidal
Density:
1.757 g/cm3 (Measured)    1.745 g/cm3 (Calculated)

Optical Data of Hexahydrite

Type:
Biaxial (-)
RI values:
nα = 1.426 nβ = 1.453 nγ = 1.456
2V:
Measured: 38° , Calculated: 36°
Max Birefringence:
δ = 0.030
Image shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:
Moderate
Dispersion:
none

Chemical Properties of Hexahydrite

Formula:
MgSO4 · 6H2O
Elements listed in formula:
Analytical Data:
Reportedly dehydrates to starkeyite in dry air (Chou, 2005). May increase hydration to epsomite in humid air.

Crystallography of Hexahydrite

Crystal System:
Monoclinic
Class (H-M):
2/m - Prismatic
Space Group:
P2/m
Cell Parameters:
a = 24.44 Å, b = 7.21 Å, c = 10.11 Å
β = 98.28°
Ratio:
a:b:c = 3.39 : 1 : 1.402
Unit Cell Volume:
V 1,762.94 ų (Calculated from Unit Cell)
Morphology:
Good crystals rare; sometimes thick tabular {001}. Also coarse columnar to delicately fibrous to acicular.
Twinning:
1. On {001}; 2. on {110}.
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:
d-spacingIntensity
5.45 (50)
5.10 (45)
4.88 (30)
4.39 (100)
4.16 (35)
4.04 (45)
2.94 (30)
(
Comments:
ICDD 24-719

Type Occurrence of Hexahydrite

Relationship of Hexahydrite to other Species

Other Members of Group:
Bianchite(Zn,Fe)SO4 · 6H2O
Chvaleticeite(Mn,Mg)SO4 · 6H2O
FerrohexahydriteFeSO4 · 6H2O
Moorhouseite(Co,Ni,Mn)SO4 · 6H2O
Nickelhexahydrite(Ni,Mg,Fe)SO4 · 6H2O
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.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.85PickeringiteMgAl2(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
25.3.6EpsomiteMgSO4 · 7H2O
25.3.7CaminiteMg7(SO4)5(OH)4 · H2O
25.3.8VanthoffiteNa6Mg(SO4)4
25.3.9BlöditeNa2Mg(SO4)2 · 4H2O
25.3.10KonyaiteNa2Mg(SO4)2 · 5H2O
25.3.11LöweiteNa12Mg7(SO4)13 · 15H2O
25.3.12UklonskoviteNaMg(SO4)F · 2H2O
25.3.13LangbeiniteK2Mg2(SO4)3
25.3.14LeoniteK2Mg(SO4)2 · 4H2O
25.3.15PicromeriteK2Mg(SO4)2 · 6H2O
25.3.16Efremovite(NH4)2Mg2(SO4)3
25.3.17Boussingaultite(NH4)2Mg(SO4)2 · 6H2O
25.3.18PickeringiteMgAl2(SO4)4 · 22H2O

Other Names for Hexahydrite

Name in Other Languages:
German:Hexahydrit
Simplified Chinese:六水泻盐
六水镁矾
Spanish:Hexahydrita
Traditional Chinese:六水瀉鹽
六水鎂礬

Other Information

Fluoresces and phosphoresces dull cream white (Sterling Mine, Ogdensburg, NJ, USA).
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 Hexahydrite

Reference List:
Johnston (1911) Geological Survey of Canada, Summary Report 1910: 256.
Walker and Parsons (1927) University of Toronto Stud., Geology Service: 24: 21.
Dolivo-Dobrovolsky (1929) Mineralogicheskoe Obshchestvo, Leningrad, Zapiski: [2]: 58: 3.
Kokta (1935) Publ. Fac. Science, University Masaryk, Brno: 166.

Palache, C., Berman, H., and 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.: 494-495.
Acta Crystallographica: 17: 235-240.
Mineralogical Abstracts: 74 (1974): 3459.
Chou, I. Ming (2005)Determination Of Hexahydrite-Starkeyite Equilibria By The Humidity-Buffer Technique At 0.1 Mpa: Implications For The Martian H2O Cycle, Geological Society of America Abstracts with Programs, Vol. 37, No. 7, p. 55

Internet Links for Hexahydrite

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https://www.mindat.org/min-1891.html
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Localities for Hexahydrite

map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the symbol to view information about a locality. The symbol next to localities in the list can be used to jump to that position on the map.
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