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Eugene Woldemar Hilgard
Ca2B5O9Cl · H2O
Colorless, light pink; colourless in transmitted light
Specific Gravity:
2.67 - 2.71
Crystal System:
Named for Eugene Woldemar Hilgard (1833-1916), German-American geologist, one of the first to describe the Louisiana salt dome deposits.
Hilgardite Group.

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

Hide all sections | Show all sections

Classification of HilgarditeHide

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

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

5 : Pentaborates

10 : Borates with other anions
1 : Borates with halide

Physical Properties of HilgarditeHide

Colorless, light pink; colourless in transmitted light
Perfect on the {010}, also on {100} but more difficult to realize.
2.67 - 2.71 g/cm3 (Measured)    2.69 g/cm3 (Calculated)

Optical Data of HilgarditeHide

Biaxial (+)
RI values:
nα = 1.630 nβ = 1.636 nγ = 1.664
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:
r > v

Chemical Properties of HilgarditeHide

Ca2B5O9Cl · H2O

Crystallography of HilgarditeHide

Crystal System:
Class (H-M)
Space Group:
Space Group Setting:
Cell Parameters:
Unit Cell Volume (calc):
 Triclinic Monoclinic 
 1 - Pedialm - Domatic

a = 11.24 Å, b = 22.28 Å, c = 6.2 Å
α = 90°, β = 90°, γ = 91.2°
a = 11.470(3) Å, b = 11.321(4) Å, c = 6.321(5) Å
β = 90.02(7)°
 a:b:c = 0.504 : 1 : 0.278a:b:c = 1.013 : 1 : 0.558
 V 1,552.31 ų
(Calculated from Unit Cell)
V 820.79 ų
(Calculated from Unit Cell)

Type Occurrence of HilgarditeHide

Synonyms of HilgarditeHide

Other Language Names for HilgarditeHide

Simplified Chinese:氯羟硼钙石
Traditional Chinese:氯羥硼鈣石

Varieties of HilgarditeHide

Strontiohilgardite-1TcA strontium-bearing (strontian) hilgardite-1Tc.

Relationship of Hilgardite to other SpeciesHide

Other Members of this group:
KurgantaiteCaSr[B5O9]Cl · H2OTric. 1 : P1
LeucostauritePb2[B5O9]Cl · 0.5H2OOrth. mm2 : Pnn2
TyretskiteCa2B5O9OH · H2OTric.

Common AssociatesHide

Associated Minerals Based on Photo Data:
Boracite30 photos of Hilgardite associated with Boracite on
Volkovskite9 photos of Hilgardite associated with Volkovskite on
Hilgardite-3Tc4 photos of Hilgardite associated with Hilgardite-3Tc on

Related Minerals - Nickel-Strunz GroupingHide

6.ED.05TyretskiteCa2B5O9OH · H2OTric.
6.ED.05KurgantaiteCaSr[B5O9]Cl · H2OTric. 1 : P1

Related Minerals - Hey's Chemical Index of Minerals GroupingHide

10.1.1TeepleiteNa2[B(OH)4]ClTet. 4/mmm (4/m 2/m 2/m) : P4/nmm
10.1.2BandyliteCu[B(OH)4]ClTet. 4/mmm (4/m 2/m 2/m) : P4/nmm
10.1.3BerboriteBe2(BO3)(OH,F) · H2OTrig.
10.1.5BoraciteMg3(B7O13)ClOrth. mm2 : Pca21
10.1.7ShabyniteMg5(BO3)(OH)5(Cl,OH)2 · 4H2OMon.
10.1.12HydrochlorboriteCa4B8O15Cl2 · 21H2OMon.
10.1.13EkateriniteCa2(B4O7)(Cl,OH)2 · 2H2OHex.
10.1.14VolkovskiteKCa4[B5O8OH]4[B(OH)3]2Cl · 4H2OTric. 1 : P1
10.1.15ChelkariteCaMgB2O4(Cl,OH)2 · 5H2O Or near, with Cl:OH = 3:1Orth.
10.1.16JohachidoliteCaAlB3O7Orth. mmm (2/m 2/m 2/m) : Cmma
10.1.17SatimoliteKNa2Al4[Cl|B2O5]3 · 13H2OOrth.
10.1.18ChambersiteMn2+3(B7O13)ClOrth. mm2 : Pca21
10.1.19Congolite(Fe2+,Mg)3(B7O13)ClTrig. 3m : R3c

Other InformationHide

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 HilgarditeHide

Reference List:
Sort by Year (asc) | by Year (desc) | by Author (A-Z) | by Author (Z-A)
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:]
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 HilgarditeHide

Localities for HilgarditeHide

This 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.

Locality ListHide

- This locality has map coordinates listed. - This locality has estimated coordinates. ⓘ - Click for further information on this occurrence. ? - Indicates mineral may be doubtful at this locality. - Good crystals or important locality for species. - World class for species or very significant. (TL) - Type Locality for a valid mineral species. (FRL) - First Recorded Locality for everything else (eg varieties). Struck out - Mineral was erroneously reported from this locality. Faded * - Never found at this locality but inferred to have existed at some point in the past (eg from pseudomorphs.)

All localities listed without proper references should be considered as questionable.
  • 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.
  • Yunnan Province
    • Pu'er Prefecture
      • Jiangcheng Co.
[Hilgardite-3Tc] Li, M., Yan, M., Wang, Z., Liu, X., Fang, X., & Li, J. (2015). The origins of the Mengye potash deposit in the Lanping–Simao Basin, Yunnan Province, Western China. Ore Geology Reviews, 69, 174-186.
  • Lower Saxony
    • Göttingen
      • Reyershausen
[Clark, 1993 - "Hey's Mineral Index"]
  • Southern District (HaDarom District)
Anthony, et al (2003) Handbook of Mineralogy, Vol. 5, p. 288.
  • 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; ERCOSPAN (2011) Independent Geological Report on the Zhilianskoe and Chelkar Potash Deposits in Kazakhstan EGB 11-012
  • 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.
  • Eastern-Siberian Region
    • Prebaikalia (Pribaikal'e)
      • Irkutskaya Oblast'
        • Lena-Angara salt Basin
Dimitri Belakovski
        • Zheleznogorsk (Korshunikha)
Mazurov, M.P., Grishina, S.N., Istomin, V.E., and Titov, A.T. (2007): Geology of Ore Deposits 49(4), 271-284.
  • Central Anatolia Region
    • Eskişehir Province
      • Kirka
[Hilgardite-4M] Koçak, İ. & Koç, Ş. (2016): Geochemical characteristics of Kırka (Sarıkaya) borate deposit, northwestern Anatolia, Turkey. Journal of Earth System Science: 125: 147-164; (2016)
  • England
    • North Yorkshire
      • Loftus
BMS Collection hilgardite-1TC; UK Journal of Mines and Minerals, No. 14 p4-7
Smith, F.W., Dearlove, J.P.L., Kemp, S.J., Bell, C.P., Milne, C.J. and Pottas, T.L. (2014) Potash – Recent exploration developments in North Yorkshire. Pp. 45-50 in Hunger, E., Brown, T. J. and Lucas, G. (Eds.) Proceedings of the 17th Extractive Industry Geology Conference, EIG Conferences Ltd. 202pp
Smith, F.W., Dearlove, J.P.L., Kemp, S.J., Bell, C.P., Milne, C.J. and Pottas, T.L. (2014) Potash – Recent exploration developments in North Yorkshire. Pp. 45-50 in Hunger, E., Brown, T. J. and Lucas, G. (Eds.) Proceedings of the 17th Extractive Industry Geology Conference, EIG Conferences Ltd. 202pp
  • 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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