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Hilgardite

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Boulby Mine, Loftus, North Yorkshire, England, UK
© Leon Hupperichs

Show Hilgardite Photos (7)
Formula:
Ca
 
2
B
 
5
O
 
9
Cl·H
 
2
O
System:TriclinicColour:Colorless, light pink; ...
Hardness:5
Name:
Named for Eugene Woldemar Hilgard (1833-1916), German-American geologist, one of the first to describe the Loiuisiana salt dome deposits.
This page provides mineralogical data about Hilgardite.

Classification of Hilgardite

IMA status:Approved
Strunz 8th edition ID:5/K.04-10
Nickel-Strunz 10th (pending) edition ID:6.ED.05

6 : BORATES
E : Pentaborates
D : Tekto-pentaborates
Dana 7th edition ID:26.5.14.1
Dana 8th edition ID:26.5.14.1

26 : HYDRATED BORATES CONTAINING HYDROXYL OR HALOGEN
5 : Pentaborates
Hey's CIM Ref.:10.1.8/9/10

10 : Borates with other anions
1 : Borates with halide
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Type Occurrence of Hilgardite

Type Locality:Choctaw Salt Dome, Iberville Parish, Louisiana, USA
Year of Discovery:1937
Geological Setting of type material:Salt dome.
Associated Minerals at type locality:
QuartzPyriteMagnesiteHilgardite-3TcHauerite
DolomiteDanburiteCalciteBoraciteAnhydrite

Occurrences of Hilgardite

Geological Setting:Marine evaporite deposits

Physical Properties of Hilgardite

Lustre:Vitreous
Diaphaneity (Transparency):Transparent
Colour:Colorless, light pink; colourless in transmitted light
Streak:White
Hardness (Mohs):5
Cleavage:Perfect
Perfect on the {010}, also on {100} but more difficult to realize.
Fracture:Conchoidal
Density (measured):2.67 - 2.71 g/cm3
Density (calculated):2.69 g/cm3

Crystallography of Hilgardite

Crystal System:Triclinic
Class (H-M):1 - Pedial
Space Group:P1
Cell Parameters:a = 6.297Å, b = 6.464Å, c = 6.565Å
α = 74.24°, β = 61.68°, γ = 61.26°
Ratio:a:b:c = 0.974 : 1 : 1.016
Unit Cell Volume:V 198.5 ų
Z:1
Morphology:Crystals tabular {010}, with a marked hemimorphic aspect.
Comment:1A polytype

Optical Data of Hilgardite

Type:Biaxial (+)
RI values: nα = 1.630 nβ = 1.636 nγ = 1.664
2V:Measured: 35° , Calculated: 52°
Maximum Birefringence:δ = 0.034

Chart shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:Moderate
Dispersion:r > v

Chemical Properties of Hilgardite

Formula:
Ca
 
2
B
 
5
O
 
9
Cl·H
 
2
O
Essential elements:B, Ca, Cl, H, O
All elements listed in formula:B, Ca, Cl, H, O

Relationship of Hilgardite to other Species

Related Minerals - Nickel-Strunz Grouping):

- +
6.ED.05Tyretskite
Ca
 
2
B
 
5
O
 
9
OH·H
 
2
O
6.ED.05Kurgantaite
CaSr[B
 
5
O
 
9
]Cl · H
 
2
O
Related Minerals - Hey's Index Grouping:

- +
10.1.1Teepleite
Na
 
2
[Cl|B(OH)
 
4
]
10.1.2Bandylite
Cu[Cl|B(OH)
 
4
]
10.1.3Berborite
Be
 
2
[(OH,F)|BO
 
3
] · H
 
2
O
10.1.4Fluoborite
Mg
 
3
[(F,OH)
 
3
|BO
 
3
]
10.1.5Boracite
Mg
 
3
[Cl|B
 
7
O
 
13
]
10.1.6Karlite
Mg
 
7
[(OH,Cl)
 
5
|(BO
 
3
)
 
3
]
10.1.7Shabynite
Mg
 
5
[(Cl,OH)
 
2
|(OH)
 
5
|BO
 
3
] · 4H
 
2
O
10.1.11Solongoite
Ca
 
2
(H
 
3
B
 
3
O
 
7
)(OH)Cl
10.1.12Hydrochlorborite
Ca
 
4
B
 
8
O
 
15
Cl
 
2
·21H
 
2
O
10.1.13Ekaterinite
Ca
 
2
[(Cl,OH)
 
2
|B
 
4
O
 
7
] · 2H
 
2
O
10.1.14Volkovskite
KCa
 
4
[B
 
5
O
 
8
OH]
 
4
[B(OH)
 
3
]
 
2
Cl·4H
 
2
O
10.1.15Chelkarite
CaMgB
 
2
O
 
4
(Cl,OH)
 
2
·5H
 
2
O Or near, with Cl:OH = 3:1
10.1.16Johachidolite
CaAlB
 
3
O
 
7
10.1.17Satimolite
KNa
 
2
Al
 
4
[Cl|B
 
2
O
 
5
]
 
3
 · 13H
 
2
O
10.1.18Chambersite
Mn
2+
3
[Cl|B
 
7
O
 
13
]
10.1.19Congolite
(Fe
2+
 
,Mg)
 
3
B
 
7
O
 
13
Cl
10.1.20Ericaite
Fe
2+
3
[Cl|B
 
7
O
 
13
]

Other Names for Hilgardite

Other Languages:
German:Hilgardit
Russian:Хилгардит
Spanish:Hilgardita
Varieties:
StrontiohilgarditeStrontiohilgardite-1Tc

Polytypes for Hilgardite

Polytypes:
Hilgardite-1TcHilgardite-3TcHilgardite-4M

Other Information

Electrical:Piezoelectric
Health Warning:No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

References for Hilgardite

Reference List:Hurlbut and Taylor (1937) American Mineralogist: 22: 1052-1057.

Taylor (1937) Bulletin of the American Association of Petr. Geol.: 21: 1268.

American Mineralogist (1938): 23: 765-771.

Palache, Charles, Harry Berman & Clifford Frondel (1951), The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana Yale University 1837-1892, Volume II: Halides, Nitrates, Borates, Carbonates, Sulfates, Phosphates, Arsenates, Tungstates, Molybdates, Etc. John Wiley and Sons, Inc., New York, 7th edition, revised and enlarged, 1124pp.: 382-383.

American Mineralogist (1984): 69: 214.

Ghose, S. (1985) A new nomenclature for the borate minerals in the hilgardite (Ca2B5O9Cl·H2O)-tyretskite (Ca2B5O9OH·H2O) group. American Mineralogist (1985): 70: 636-637.

Rachlin, A.L., Mandarino, J.., Murowchick, B.L., Ramik, R.A., Dunn, P.J., and Bac, M.E. (1986) Mineralogy of hilgardite-4M from evaporites in New Brunswick. Canadian Mneralogist: 24: 689-693.

Burns, P.C. and Hawthorne, F.C. (1994) Refinement of the structure of hilgardite-1A. Acta Crystallographica: C50: 653-655.

Grew, E.S., and Anovitz, L.M. (1996) BORON: Mineralogy, Petrology and Geochemistry, second edition, as revised (2002).

Internet Links for Hilgardite

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  • Raman and XRD data at RRUFF project
  • American Mineralogist Crystal Structure Database
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  • Hilgardite details from Handbook of Mineralogy (PDF)
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    Localities for Hilgardite

    Hide Locality List
    The 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.
    (TL) indicates type locality. ? indicates mineral may be doubtful at this locality. All other localities listed without reference should be considered as uncertain and unproven until references can be found.
    Canada
     
    • New Brunswick
      • Kings Co.
    		Canadian Mineralogist: 43: 1469-1487.
        • Sussex
          • Cardwell Parish
            • Penobsquis
    		Canadian Mineralogist (1996): 34: 657-665.
    P.C. Burns, F.C. Hawthorne, J.A.R. Stirling: Can. Mineral. 30:445-448 (1992)
    Germany
     
    • Lower Saxony
      • Göttingen
        • Reyershausen
    		[Clark, 1993 - "Hey's Mineral Index"]
    Kazakhstan
     
    • Aqtöbe Oblysy (Aktubinsk [Aktyubinsk; Aktubinskaya] Oblast')
      • Aksai Valley
    		Pekov, I. (1998) Minerals First discovered on the territory of the former Soviet Union 369p. Ocean Pictures, Moscow
    • Atyrau Oblysy (Atyrau Oblast')
      • Atyrau (Gur'yev)
    		Pekov, I. (1998) Minerals First discovered on the territory of the former Soviet Union 369p. Ocean Pictures, Moscow
    Russia
     
    • Eastern-Siberian Region
      • Prebaikalia (Pribaikal'e)
        • Irkutskaya Oblast'
    		Mazurov, M.P., Grishina, S.N., Istomin, V.E., and Titov, A.T. (2007): Geology of Ore Deposits 49(4), 271-284.
    UK
     
    • England
      • North Yorkshire
        • Loftus
    		BMS Collection hilgardite-1TC; UK Journal of Mines and Minerals, No. 14 p4-7
    USA
     
    • Alabama
      • Clarke Co.
    		Rocks & Min.: 64:472.
    • Louisiana
      • Iberville Parish
    		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: 380, 383; Clark, 1993 - "Hey's Mineral Index".
    Mineral and/or Locality
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