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Hilgardite

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Eugene Woldemar Hilgard
Formula:
Ca2B5O9Cl · H2O
System:
Triclinic
Colour:
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.
Hilgardite Group.

Several polytypes are known, as well as Sr-bearing varieties.

Classification of Hilgardite

Approved
6.ED.05

6 : BORATES
E : Pentaborates
D : Tekto-pentaborates
Dana 7th ed.:
26.5.14.1
26.5.14.1

26 : HYDRATED BORATES CONTAINING HYDROXYL OR HALOGEN
5 : Pentaborates
10.1.8/9/10

10 : Borates with other anions
1 : Borates with halide
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First Recorded Occurrence of Hilgardite

Year of Discovery:
1937
Geological Setting of First Recorded Material:
Salt dome.

Occurrences of Hilgardite

Geological Setting:
Marine evaporite deposits

Physical Properties of Hilgardite

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:
2.67 - 2.71 g/cm3 (Measured)    2.69 g/cm3 (Calculated)

Crystallography of Hilgardite

Polytype:
Formula:
Crystal System:
Class (H-M)
Space Group:
Space Group Setting:
Cell Parameters:
Ratio:
Unit Cell Volume (calc):
Z:
Hilgardite-1TcHilgardite-3TcHilgardite-4M
 Triclinic  
1 - Pedial
 P1 
   

a = 11.24Å, b = 22.28Å, c = 6.2Å
α = 90°, β = 90°, γ = 91.2°

a:b:c = 0.504 : 1 : 0.278
 2 

Optical Data of Hilgardite

Type:
Biaxial (+)
RI values:
nα = 1.630 nβ = 1.636 nγ = 1.664
2V:
Measured: 35° , Calculated: 52°
Max Birefringence:
δ = 0.034
Image 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:
Ca2B5O9Cl · H2O
Essential elements:
All elements listed in formula:

Relationship of Hilgardite to other Species

Other Members of Group:
KurgantaiteCaSr[B5O9]Cl · H2O
LeucostauritePb2[B5O9]Cl · 0.5H2O
TyretskiteCa2B5O9OH · H2O
6.ED.05TyretskiteCa2B5O9OH · H2O
6.ED.05KurgantaiteCaSr[B5O9]Cl · H2O
10.1.1TeepleiteNa2[B(OH)4]Cl
10.1.2BandyliteCu[B(OH)4]Cl
10.1.3BerboriteBe2(BO3)(OH,F) · H2O
10.1.4FluoboriteMg3(BO3)(F,OH)3
10.1.5BoraciteMg3(B7O13)Cl
10.1.6KarliteMg7(BO3)3(OH,Cl)5
10.1.7ShabyniteMg5(BO3)(OH)5(Cl,OH)2 · 4H2O
10.1.11SolongoiteCa2(H3B3O7)(OH)Cl
10.1.12HydrochlorboriteCa4B8O15Cl2 · 21H2O
10.1.13EkateriniteCa2(B4O7)(Cl,OH)2 · 2H2O
10.1.14VolkovskiteKCa4[B5O8OH]4[B(OH)3]2Cl · 4H2O
10.1.15ChelkariteCaMgB2O4(Cl,OH)2 · 5H2O Or near, with Cl:OH = 3:1
10.1.16JohachidoliteCaAlB3O7
10.1.17SatimoliteKNa2Al4[Cl|B2O5]3 · 13H2O
10.1.18ChambersiteMn32+(B7O13)Cl
10.1.19Congolite(Fe2+,Mg)3(B7O13)Cl
10.1.20EricaiteFe32+(B7O13)Cl

Other Names for Hilgardite

Name in Other Languages:
German:Hilgardit
Simplified Chinese:氯羟硼钙石
Spanish:Hilgardita
Traditional Chinese:氯羥硼鈣石

Other Information

Electrical:
Piezoelectric
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 Hilgardite

Reference List:
Hurlbut, C. S. & Taylor, R. E. (1937): Hilgardite, a new mineral species from Choctaw Salt Dome, Louisiana. 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.

Braitsch, O. (1959) 1Tc-Strontiohilgardite (Ca,Sr)2[B5O9](OH)2Cl and seine Stellung in the Hilgarditgruppe. Beiträge Mineral. und Petrogr.: 6: 233-247. [Abs. in Am. Mineral. 44, 1102: http://www.minsocam.org/ammin/AM44/AM44_1102.pdf]

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

Specimens:
The following Hilgardite specimens are currently listed for sale on minfind.com.

Localities for Hilgardite

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 for a valid mineral species. (FRL) indicates first recorded locality for everything else. ? 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.
      • Cardwell Parish
        • Penobsquis
Canadian Mineralogist (1996): 34: 657-665.; Canadian Mineralogist (1996): 34: 881-892
      • Hammond Parish
        • Salt Springs evaporite deposit
P.C. Burns, F.C. Hawthorne, J.A.R. Stirling: Can. Mineral. 30:445-448 (1992); Roulston, B.V. and Waugh, D.C.E. (1981) A borate mineal assemblage from the Penobsquis and Salt Springs evaporite deposits of southern New Brunswick. Canadian Mineralogist: 19: 291-301.
      • Studholm Parish
Canadian Mineralogist: 43: 1469-1487.
Germany
 
  • Lower Saxony
    • Göttingen
      • Reyershausen
[Clark, 1993 - "Hey's Mineral Index"]
Israel
 
  • Southern District (HaDarom District)
Anthony, et al (2003) Handbook of Mineralogy, Vol. 5, p. 288.
Kazakhstan
 
  • Aktobe Province (Aqtöbe Oblysy; Aktubinskaya Oblast')
    • Aksai Valley
Pekov, I. (1998) Minerals First discovered on the territory of the former Soviet Union 369p. Ocean Pictures, Moscow
  • Atyrau Province (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; Evseev, A. A. (1995) Kazaknstan and Middle Asia. A brief Mineralogical Guide. World of Stone 8:24-30; Pekov, I. V. & Abramov, D. V. (1993): Boron deposit of the Inder and its minerals. World of Stones, 1, 23-30.
Russia
 
  • Eastern-Siberian Region
    • Prebaikalia (Pribaikal'e)
      • Irkutskaya Oblast'
        • Lena-Angara salt Basin
[var: Strontiohilgardite] Dimitri Belakovski
        • Zheleznogorsk
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
      • Plaquemine
Hurlbut, C. S., Taylor, R. E. (1937): Hilgardite, a new mineral species from Choctaw Salt Dome, Louisiana. American Mineralogist. 22, 1052-1057; American Mineralogist 23:898
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