Hilgardite
A valid IMA mineral species - grandfathered
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About Hilgardite
Eugene W. Hilgard
Formula:
Ca2B5O9Cl · H2O
Colour:
Colorless, light pink; colourless in transmitted light
Lustre:
Vitreous
Hardness:
5
Specific Gravity:
2.67 - 2.71
Crystal System:
Triclinic
Member of:
Name:
Named for Eugene Woldemar Hilgard (5 January 1833, Zweibrücken, Rhineland-Palatinate, Germany – 8 January 1916, Berkeley, California, United States), German-American geologist, one of the first to describe the Louisiana salt dome deposits. He is also considered the father of modern soil science in the United States.
Unique Identifiers
Mindat ID:
1902
Long-form identifier:
mindat:1:1:1902:2
Similar Names
| Hilgardite-1A | A synonym of 'Hilgardite-1Tc' |
| Hilgardite-3A | A synonym of 'Hilgardite-3Tc' |
IMA Classification of Hilgardite
Approved, 'Grandfathered' (first described prior to 1959)
IMA Formula:
Ca2B5O9Cl·H2O
First published:
1937
Classification of Hilgardite
6.ED.05
6 : BORATES
E : Pentaborates
D : Tekto-pentaborates
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
26 : HYDRATED BORATES CONTAINING HYDROXYL OR HALOGEN
5 : Pentaborates
10.1.8/9/10
10 : Borates with other anions
1 : Borates with halide
10 : Borates with other anions
1 : Borates with halide
Mineral Symbols
As of 2021 there are now IMA–CNMNC approved mineral symbols (abbreviations) for each mineral species, useful for tables and diagrams.
| Symbol | Source | Reference for Standard |
|---|---|---|
| Hgr | IMA–CNMNC | Warr, L.N. (2021). IMA–CNMNC approved mineral symbols. Mineralogical Magazine, 85(3), 291-320. doi:10.1180/mgm.2021.43 |
Physical Properties of Hilgardite
Vitreous
Transparency:
Transparent
Colour:
Colorless, light pink; colourless in transmitted light
Streak:
White
Hardness:
5 on Mohs scale
Cleavage:
Perfect
Perfect on the {010}, also on {100} but more difficult to realize.
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)
Optical Data of Hilgardite
Type:
Biaxial (+)
RI values:
nα = 1.63 nβ = 1.636 nγ = 1.664
2V:
Measured: 35° , Calculated: 52°
Max. Birefringence:
δ = 0.034
Based on recorded range of RI values above.
Based on recorded range of RI values above.
Interference Colours:
The colours simulate birefringence patterns seen in thin section under crossed polars. They do not take into account mineral colouration or opacity.
Michel-Levy Bar The default colours simulate the birefringence range for a 30 µm thin-section thickness. Adjust the slider to simulate a different thickness.
Grain Simulation You can rotate the grain simulation to show how this range might look as you rotated a sample under crossed polars. Each grain retains its interference colour (retardation) while its brightness falls to black at extinction and reaches a maximum between extinction positions.
The colours simulate birefringence patterns seen in thin section under crossed polars. They do not take into account mineral colouration or opacity.
Michel-Levy Bar The default colours simulate the birefringence range for a 30 µm thin-section thickness. Adjust the slider to simulate a different thickness.
Grain Simulation You can rotate the grain simulation to show how this range might look as you rotated a sample under crossed polars. Each grain retains its interference colour (retardation) while its brightness falls to black at extinction and reaches a maximum between extinction positions.
Surface Relief:
High (positive)
Relative to Canada balsam mounting medium (n ≈ 1.537).
Relative to Canada balsam mounting medium (n ≈ 1.537).
This shows the grain boundary and Becke line effect under plane-polarised
light, based on the contrast between this mineral's average refractive
index and the mounting medium. It does not take into account mineral
colouration.
In focus
Interference Figure:
This shows the idealized biaxial acute bisectrix (Bxa) interference figure
- the conoscopic view for a grain cut perpendicular to the acute bisectrix, using
this mineral's 2V. The two small white dots mark the melatopes - the points
where the two optic axes emerge - and are shown only when they fall within the
field of view. The coloured bands are isochromatics, and the dark bands are
isogyres.
Rotate the stage: at 0°/90° the isogyres form a cross through the melatopes; at 45° they pull apart into curved hyperbolas. That splitting on rotation - absent in a uniaxial figure - is the standard diagnostic test for telling biaxial minerals from uniaxial ones. If 2V is large, the melatopes may fall outside the field of view, as they often do at the microscope too.
Rotate the stage: at 0°/90° the isogyres form a cross through the melatopes; at 45° they pull apart into curved hyperbolas. That splitting on rotation - absent in a uniaxial figure - is the standard diagnostic test for telling biaxial minerals from uniaxial ones. If 2V is large, the melatopes may fall outside the field of view, as they often do at the microscope too.
Dispersion:
r > v
Chemistry of Hilgardite
Mindat Formula:
Ca2B5O9Cl · H2O
Element Weights:
Crystallography of Hilgardite
Polytype:
Formula:
Crystal System:
Class (H-M)
Space Group:
Space Group Setting:
Cell Parameters:
Ratio:
Unit Cell Volume (calc):
Z:
Comment:
| Hilgardite-1Tc | Hilgardite-3Tc | Hilgardite-4M |
|---|---|---|
| Ca2B5O9Cl · H2O | Ca2B5O9Cl · H2O | Ca2B5O9Cl · H2O |
| Triclinic | Triclinic | Monoclinic |
| 1 - Pedial | m - Domatic | |
| P1 | ||
| 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 : 0.278 | a:b:c = 1.013 : 1 : 0.558 | |
| V 1,552.31 ų (Calculated from Unit Cell) | V 820.79 ų (Calculated from Unit Cell) | |
| 1 | 2 | |
| Space group Aa. |
Crystal Structure
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Unit Cell | Unit Cell Packed
2x2x2 | 3x3x3 | 4x4x4
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Data courtesy of the American Mineralogist Crystal Structure Database. Click on an AMCSD ID to view structure
| ID | Species | Reference | Link | Year | Locality | Pressure (GPa) | Temp (K) |
|---|---|---|---|---|---|---|---|
| 0010290 | Hilgardite | Burns P C, Hawthorne F C (1994) Refinement of the structure of hilgardite-1A Acta Crystallographica C50 653-655 |  | 1994 | Penobsquis potash deposit, Sussex, New Brunswick | 0 | 293 |
| 0000901 | Hilgardite | Wan C, Ghose S (1983) Parahilgardite, Ca6[B5O9]3Cl3*3H2O: a triclinic piezoelectric zeolite-type pentaborate American Mineralogist 68 604-613 |  | 1983 | Iberville Parish, Louisiana, USA | 0 | 293 |
| 0000696 | Hilgardite | Ghose S, Wan C (1979) Hilgardite, Ca2[B5O9]Cl*H2O: a piezoelectric zeolite-type pentaborate American Mineralogist 64 187-195 | | 1979 | Choctow Salt Dome, Iberville Parish, Louisiana, USA | 0 | 293 |
| 0015604 | Hilgardite | Rumanova I M, Iorysh Z I, Belov N V (1977) Crystal structure of triclinic chilgardite Ca2[B5O9]Cl*H2O = Ca2[B3+-B2deltaO9]Cl*H2O Soviet Physics Doklady 22 460-462 | 1977 | not given | 0 | 293 |
CIF Raw Data - click here to close
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| - Å | () |
Comments:
X-ray powder diffraction data can be found on the polytype pages.
Geological Environment
Paragenetic Mode(s):
| Paragenetic Mode | Earliest Age (Ga) |
|---|---|
| Near-surface Processes | |
| 25 : Evaporites (prebiotic) |
Geological Setting:
Marine evaporite deposits
Type Occurrence of Hilgardite
Place of Conservation of Type Material:
Harvard University, Cambridge, Massachusetts, USA, 100899, 100947, 106583.
National Museum of Natural History (Smithsonian), Washington, D.C., USA, R7822.
National Museum of Natural History (Smithsonian), Washington, D.C., USA, R7822.
Geological Setting of Type Material:
Salt dome.
Associated Minerals at Type Locality:
Synonyms of Hilgardite
Other Language Names for Hilgardite
Dutch:Hilgardiet
German:Hilgardit
Russian:Хилгардит
Simplified Chinese:氯羟硼钙石
Spanish:Hilgardita
Traditional Chinese:氯羥硼鈣石
Varieties of Hilgardite
| Strontiohilgardite | |
| Strontiohilgardite-1Tc | A strontium-bearing (strontian) hilgardite-1Tc. |
Relationship of Hilgardite to other Species
Member of:
Other Members of Hilgardite Group:
| Kurgantaite | CaSr[B5O9]Cl · H2O | Tric. 1 : P1 |
| Leucostaurite | Pb2[B5O9]Cl · 0.5H2O | Orth. mm2 : Pnn2 |
| Tyretskite | Ca2B5O9OH · H2O | Tric. 1 : P1 |
Common Associates
Associations Based on Photo Data:
| 97 photos of Hilgardite associated with Boracite | Mg3(B7O13)Cl |
| 21 photos of Hilgardite associated with Volkovskite | KCa4[B5O8OH]4[B(OH)3]2Cl · 4H2O |
| 4 photos of Hilgardite associated with 'Hilgardite-3Tc' | Ca2B5O9Cl · H2O |
| 1 photo of Hilgardite associated with Magnesite | MgCO3 |
Related Minerals - Strunz-mindat Grouping
| 6.ED.05 | Kurgantaite | CaSr[B5O9]Cl · H2O |
| 6.ED.05 | Tyretskite | Ca2B5O9OH · H2O |
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.
Internet Links for Hilgardite
mindat.org URL:
https://www.mindat.org/min-1902.html
Please feel free to link to this page.
Please feel free to link to this page.
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References for Hilgardite
Reference List:
Hurlbut, Cornelius S., Taylor, and Ralph E. (1937) Hilgardite, a new mineral species, from Choctaw salt dome, Louisiana. American Mineralogist, 22 (10) 1052-1057
Hurlbut, Cornelius S., Taylor, and Ralph E. (1937) Hilgardite, a new mineral species, from Choctaw salt dome, Louisiana. American Mineralogist, 22 (10) 1052-1057
Hurlbut, Cornelius S. (1938) Parahilgardite, a new triclinic-pedial mineral. American Mineralogist, 23 (11) 765-771
Braitsch, Otto (1959) 1Tc-Strontiohilgardit (Ca, Sr)2[B5O8(OH)2Cl] und seine Stellung in der Hilgarditgruppe X2/II[B5O8(OH)2Cl]. Beiträge zur Mineralogie und Petrographie, 6 (4) 233-247 doi:10.1007/bf01130326
Dunn, Pete J., Grice, Joel D. Fleischer, Michael, Pabst, Adolf (1984) New mineral names. American Mineralogist, 69 (1-2) 210-215
Ghose, Subrata (1985) A new nomenclature for the borate minerals in the hilgardite (Ca2B5O9Cl·H2O)-tyretskite (Ca2B5O9OH·H2O) group. American Mineralogist, 70 (5-6) 636-637
Rachlin, Alan L., Mandarino, Joseph A., Murowchick, Bernard L., Ramik, Robert A., Dunn, Pete J., Back, Malcolm E. (1986) Mineralogy of hilgardite-4M from evaporites in New Brunswick. The Canadian Mineralogist, 24 (4) 689-693
Burns, P. C., Hawthorne, F. C. (1994) Refinement of the structure of hilgardite-1A. Acta Crystallographica Section C Crystal Structure Communications, 50 (5) 653-655 doi:10.1107/s0108270193010182
Localities for Hilgardite
Showing 28 localities.
symbol to view information about a locality.
The Locality List
- This locality has map coordinates listed.
- This locality has estimated coordinates.
ⓘ - Click for references and 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).
All localities listed without proper references should be considered as questionable.
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Boulby Mine, Loftus, Redcar and Cleveland, North Yorkshire, England, UK