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|System:||Monoclinic||Colour:||White; colourless in ...|
|Hardness:||3½ - 6½|
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. Currently in public beta-test.
Classification of Howlite
|IMA status:||Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"|
|Strunz 8th edition ID:||8/F.28-10|
|Nickel-Strunz 10th (pending) edition ID:||6.CB.20|
6 : BORATES
C : Triborates
B : Ino-triborates
|Dana 8th edition ID:||188.8.131.52|
25 : ANHYDROUS BORATES CONTAINING HYDROXYL OR HALOGEN
3 : Triborates
|Hey's CIM Ref.:||17.5.12|
17 : Silicates Containing other Anions
5 : Borosilicates
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Type Occurrence of Howlite
|Type Locality:||Black's quarry, Brookville farm, Martock, West Hants, Hants Co., Nova Scotia, Canada|
|General Appearance of Type Material:||Nodules embedded in anhydrite or gypsum.|
|Year of Discovery:||1868|
|Associated Minerals at type locality:|
Occurrences of Howlite
|Geological Setting:||In borate deposits.|
Physical Properties of Howlite
|Colour:||White; colourless in transmitted light|
|Hardness (Mohs):||3½ - 6½|
|Comment:||XLs 6.5; massive 3.5|
|Comment:||Even and smooth in porcelaneous types.|
|Density (measured):||2.53 - 2.59 g/cm3|
|Density (calculated):||2.61 g/cm3|
Crystallography of Howlite
|Class (H-M):||2/m - Prismatic|
|Cell Parameters:||a = 12.82Å, b = 9.351(1) Å, c = 8.608(2) Å|
β = 104.84(2)°
|Ratio:||a:b:c = 1.371 : 1 : 0.921|
|Unit Cell Volume:||V 997.51 Å³ (Calculated from Unit Cell)|
|Morphology:||Compact nodular masses, internally dense and structureless. Chalk-like, earthy, scaly, slaty structured.|
|X-Ray Powder Diffraction:|
Radiation - Copper Kα
Data courtesy of RRUFF project at University of Arizona, used with permission.
Optical Data of Howlite
|RI values:||nα = 1.583 - 1.586 nβ = 1.596 - 1.598 nγ = 1.600|
|2V:||Measured: 60° to 90°, Calculated: 88°|
|Maximum Birefringence:||δ = 0.017|
Chart shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Chemical Properties of Howlite
|Simplified for copy/paste:||Ca2B5SiO9(OH)5|
|Essential elements:||B, Ca, H, O, Si|
|All elements listed in formula:||B, Ca, H, O, Si|
Relationship of Howlite to other Species
|Related Minerals - Nickel-Strunz Grouping):|
|Related Minerals - Hey's Index Grouping:|
Other Names for Howlite
|Other Information:||Readily soluble in dilute acids. Gelatinous silica results from the reaction upon evaporation.|
|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 Howlite
HOW, H. (1868): Contributions to the mineralogy of Nova Scotia. III. Borates and other minerals in anhydrite and gypsum. Silicoborocalcite, a new mineral. Philosophical Magazine 35, (4th Ser.), 32-41, 218.
DANA, J.D. (1868): The System of Mineralogy (5th ed.). John Wiley & Sons, New York, N.Y. (598).
PENFIELD, S.L. & SPERRY, E.S. (1887): On the chemical composition of howlite, with a note on the Gooch method for the determination of boracic acid. American Journal of Science 134, 220-223.
FINNEY, J.J., KUMBASAR, I., KONNERT, J.A. & CLARK, J.R. (1970): Crystal structure of the calcium silicoborate, howlite. American Mineralogist 55, 716-728.
GRIFFEN, D.T. (1988): Howlite, Ca2SiB5O9(OH)5: structure refinement and hydrogen bonding. American Mineralogist 73, 1138-1144.
How (1871) Philosophical Magazine and Journal of Science: 41: 270 (as Winkworthite).
Giles (1903) Mineralogical Magazine: 13: 353.
Eakle (1911) University of California Geology Department, Bulletin 6: 179.
Murdoch, Joseph (1957), Crystallography and X-ray measurements of howlite from California: American Mineralogist: 42: 521-524.
Papezik, V.S. and Fong, C.C.K. (1975) Howlite and ulexite from the Carboniferous gypsum and anhydrite beds in western Newfoundland. Canadian Mineralogist: 13: 370-376.
Grew, E.S., and Anovitz, L.M. (1996) BORON: Mineralogy, Petrology and Geochemistry, second edition, as revised (2002).
Joyce, D.K. Gait, R.I. and Sturman, B.D. (1993) Howlite from Iona, Nova Scotia Short paper presented at the Rochester Mineralogical Symposium, Rochester, New York, 1993
Internet Links for Howlite
|Specimens:||The following Howlite specimens are currently listed for sale on minfind.com.|
Localities for Howlite
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.
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Locality Updated: Almendra, Vila Nova de Foz Côa, Guarda District, PortugalFrom Rui Nunes, 24th Nov 2014 13:53:34