Howlite
A valid IMA mineral species - grandfathered
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About Howlite
Henry How
Formula:
Ca2B5SiO9(OH)5
Colour:
White, colorless, brown
Lustre:
Sub-Vitreous
Hardness:
6½
Specific Gravity:
2.62
Crystal System:
Monoclinic
Name:
First described as silicoborocalcite by Henry How (11 July 1828, London, England - 28 September 1879, Windsor, Nova Scotia) chemist, geologist, and mineralogist. Professor of Natural History and Chemistry at King's College, Windsor, Nova Scotia, Canada. Renamed shortly afterwards to howlite by James Dwight Dana.
Type Locality:
Usually compact earthy masses and very rarely in crystals. The earthy material gives a "hardness" of 3.5 but this is just the hardness of separating the grains. The crystals give a hardness of 6.5 (see: http://www.mindat.org/mesg-7-226293.html)
Visit gemdat.org for gemological information about Howlite.
Visit gemdat.org for gemological information about Howlite.Unique Identifiers
Mindat ID:
1936
Long-form identifier:
mindat:1:1:1936:7
Similar Names
| Halite | A valid IMA mineral species - grandfathered | NaCl |
| Hallite | A synonym of 'Delessite' | |
| Hallite (of Delamétherie) | A synonym of Aluminite | |
| Hallite (of Lévy) | A synonym of 'Iron-bearing Magnesite' | |
| Hillite | A valid IMA mineral species | Ca2Zn(PO4)2 · 2H2O |
| Hoelite | A valid IMA mineral species - grandfathered | C14H8O2 |
| Howieite | A valid IMA mineral species | Na(Fe2+,Fe3+,Al,Mg)12(Si6O17)2(O,OH)10 |
| Hullite | A mixture of two or more distinct mineral species | |
| Höslite | A valid IMA mineral species - pending publication | Fe33+(VO4)2(SO4)(OH)(H2O)4 · 3H2O |
IMA Classification of Howlite
Approved, 'Grandfathered' (first described prior to 1959)
First published:
1868
Classification of Howlite
6.CB.20
6 : BORATES
C : Triborates
B : Ino-triborates
6 : BORATES
C : Triborates
B : Ino-triborates
25.3.5.1
25 : ANHYDROUS BORATES CONTAINING HYDROXYL OR HALOGEN
3 : Triborates
25 : ANHYDROUS BORATES CONTAINING HYDROXYL OR HALOGEN
3 : Triborates
17.5.12
17 : Silicates Containing other Anions
5 : Borosilicates
17 : Silicates Containing other Anions
5 : Borosilicates
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 |
|---|---|---|
| How | IMA–CNMNC | Warr, L.N. (2021). IMA–CNMNC approved mineral symbols. Mineralogical Magazine, 85(3), 291-320. doi:10.1180/mgm.2021.43 |
Pronunciation of Howlite
Pronunciation:
| Play | Recorded by | Country |
|---|---|---|
| Jolyon Ralph | United Kingdom |
Physical Properties of Howlite
Sub-Vitreous
Transparency:
Transparent
Colour:
White, colorless, brown
Streak:
White
Hardness:
6½ on Mohs scale
Comment:
crystals 6.5; massive 3.5
Comment:
Even and smooth in porcelaneous types.
Density:
2.62 g/cm3 (Measured) 2.61 g/cm3 (Calculated)
Optical Data of Howlite
Type:
Biaxial (-)
RI values:
nα = 1.583 - 1.586 nβ = 1.596 - 1.598 nγ = 1.6
2V:
Measured: 60° to 90°, Calculated: 88°
Max. Birefringence:
δ = 0.014 - 0.017
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:
Moderate (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:
none
Optical Extinction:
X = b; Z ∧ c ≃ 51°.
Chemistry of Howlite
Mindat Formula:
Ca2B5SiO9(OH)5
Element Weights:
Common Impurities:
Na,K
Crystallography of Howlite
Crystal System:
Monoclinic
Class (H-M):
2/m - Prismatic
Space Group:
P21/b
Setting:
P21/c
Cell Parameters:
a = 12.820(3) Å, b = 9.351(1) Å, c = 8.608(2) Å
β = 104.84(2)°
β = 104.84(2)°
Ratio:
a:b:c = 1.371 : 1 : 0.921
Unit Cell V:
997.5 ų
Z:
4
Morphology:
Flattened prismatic with pointed terminations. Elongated on [010] or [001].
Compact nodular masses, internally dense and structureless. Chalk-like, earthy, scaly, slaty structured.
Compact nodular masses, internally dense and structureless. Chalk-like, earthy, scaly, slaty structured.
Comment:
Cell data from Griffen (1988).
Crystal Structure
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Unit Cell | Unit Cell Packed
2x2x2 | 3x3x3 | 4x4x4
Unit Cell | Unit Cell Packed
2x2x2 | 3x3x3 | 4x4x4
Show
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CIF File Best | x | y | z | a | b | c
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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) |
|---|---|---|---|---|---|---|---|
| 0001197 | Howlite | Griffen D T (1988) Howlite, Ca2SiB5O9(OH)5: Structure refinement and hydrogen bonding American Mineralogist 73 1138-1144 |  | 1988 | 0 | 293 | |
| 0000202 | Howlite | Finney J J, Kumbasar I, Konnert J A, Clark J R (1970) Crystal structure of the calcium silicoborate, howlite American Mineralogist 55 716-728 | | 1970 | 0 | 293 |
CIF Raw Data - click here to close
X-Ray Powder Diffraction
Loading XRD data...
Data courtesy of RRUFF project at University of Arizona, used with permission.
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 6.2 Å | (100) |
| 3.10 Å | (90) |
| 3.90 Å | (80) |
| 2.04 Å | (70) |
| 2.07 Å | (50) |
| 1.794 Å | (50) |
| 12.4 Å | (40) |
Comments:
Sterling Borax mine, California, USA. Data from Murdoch (1957).
Geological Environment
Paragenetic Mode(s):
| Paragenetic Mode | Earliest Age (Ga) |
|---|---|
| Near-surface Processes | |
| 25 : Evaporites (prebiotic) |
Geological Setting:
In borate deposits. The common associates include those at Piskanya deposit (studenitsite is not a common species)
Type Occurrence of Howlite
General Appearance of Type Material:
Nodules embedded in anhydrite or gypsum.
Place of Conservation of Type Material:
No designated type material.
Geological Setting of Type Material:
Gypsum and anhydrite deposit.
Associated Minerals at Type Locality:
Synonyms of Howlite
Other Language Names for Howlite
Common Associates
Related Minerals - Strunz-mindat Grouping
| 6.CB.10 | Colemanite | Ca[B3O4(OH)3] · H2O |
| 6.CB.15 | Hydroboracite | CaMg[B3O4(OH)3]2 · 3H2O |
| 6.CB.25 | Jarandolite | Ca[B3O4(OH)3] |
Fluorescence of Howlite
May fluoresce orange or bluish white with SW or LW.
Other Information
IR Spectrum:
Piskanya material [cm-1]: 3460, 3492, 3404, 3212, 1455, 1435, 1410, 1379w, 1359, 1324, 1223, 1163, 1136, 1104, 1055sh, 1014s, 959s, 915s, 906s, 875, 831s, 761, 775, 750w, 707w, 682, 617, 595, 563w, 551w, 527, 511w, 466, 451
Thermal Behaviour:
Before the blowpipe, decrepitates strongly, and fuses readily to a clear colourless bead, making the inner flame green. In a closed tube it decrepitates and gives much water.
Notes:
Readily soluble in dilute acids. Gelatinous silica results from the reaction upon evaporation. A minute quantity with a drop of dilute HCl gives the boracic-acid test with tumeric paper.
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 Howlite
mindat.org URL:
https://www.mindat.org/min-1936.html
Please feel free to link to this page.
Please feel free to link to this page.
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External Links:
Mineral Dealers:
References for Howlite
Reference List:
Giles, W. B. (1903) Bakerite (a new borosilicate of calcium) and howlite from California. Mineralogical Magazine and Journal of the Mineralogical Society, 13 (62) 353-355 doi:10.1180/minmag.1903.013.62.12
Murdoch, Joseph (1957) Crystallography and x-ray measurements of howlite from California. American Mineralogist, 42 (7-8) 521-524
Finney, J. J., Kumbasar, Isik, Clark, Joan R. (1969) Crystal structure of howlite, Ca2SiB5O9(OH)5. Die Naturwissenschaften, 56 (1) 33-34 doi:10.1007/bf00599589
Finney, J. J., Kumbasar, Isik, Konnert, Judith A., Clark, Joan R. (1970) Crystal structure of the calcium silicoborate howlite. American Mineralogist, 55 (5-6) 716-728
Papezik, V. S., Fong, C. C. K. (1975) Howlite and ulexite from the Carboniferous gypsum and anhydrite beds in western Newfoundland. The Canadian Mineralogist, 13 (4) 370-376
Griffen, Dana T. (1988) Howlite, Ca2SiB5O9(OH)5: Structure refinement and hydrogen bonding. American Mineralogist, 73 (9-10) 1138-1144
Localities for Howlite
Showing 44 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.
Bolivia | |
| Bentz (2017) |
Canada | |
| Roulston et al. (1981) |
| Burns et al. (1992) |
| Papezik et al. (1975) |
| Papezik et al. (1975) | |
| Ronnie Van Dommelen collection. |
| Papezik et al. (1975) |
| How (1868) +2 other references |
| Papezik et al. (1975) +2 other references |
| Joyce et al. (1993) |
Germany | |
| Kühn et al. (1962) +3 other references |
| Siemroth (2008) |
Mexico | |
| Garrett (1998) +2 other references |
| Verley et al. (2011) | |
| Verley et al. (2011) | |
| Verley et al. (2011) | |
| Miranda-Gasca et al. (1998) +1 other reference |
| Garrett (1998) |
Serbia | |
| Putzolu et al. (2025) |
| Obradovic et al. (1992) |
| Obradovic et al. (1992) | |
| Papezik et al. (1975) +1 other reference | |
Slovakia | |
| Koděra et al. (1986) |
Turkey | |
| Helvaci +2 other references |
| Helvaci et al. (1991) +2 other references |
| Helvaci (1994) +3 other references |
UK | |
| Smith et al. (2014) |
| Smith et al. (2014) |
| Smith et al. (2014) | |
| Kemp et al. (2016) | |
USA | |
| Palache et al. (1951) |
| Chandler (1996) |
| www.mineralsocal.org (1999) |
| U.S. Borax | |
| Gale (1946) +1 other reference | |
| Palache et al. (1951) |
| Rocks & Minerals: 11: 156. +9 other references |
| Murdoch et al. (1966) |
| Giles (1903) +1 other reference |
| Palache et al. (1951) | |
| Dibblee (1967) +2 other references |
| Dibblee (1967) +2 other references |
| Gale (1914c) +3 other references |
| Palache et al. (1951) |
Quick NavTopAbout HowliteUnique IdentifiersSimilar NamesIMA Classification Classification Mineral SymbolsPronunciation Physical Properties Optical Data Chemistry Crystallography Crystal StructureX-Ray Powder DiffractionGeological EnvironmentType Occurrence SynonymsOther LanguagesCommon AssociatesStrunz-MindatFluorescence Other InformationInternet Links References Localities Locality List
Bras D'Or Lake howlite locality, Iona, Victoria Co., Nova Scotia, Canada