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Prehnite

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Formula:
Ca2Al2Si3O10(OH)2
Colour:
Colourless to gray to yellow, yellow-green or white
Lustre:
Vitreous, Pearly
Hardness:
6 - 6½
Specific Gravity:
2.8 - 2.95
Crystal System:
Orthorhombic
Name:
Named in 1788 by Abraham Gottlieb Werner in honor of the Dutch Colonel, Hendrik von/van Prehn [July 31/August 2, 1733 Cape of Good Hope Colony - August 1785 Heilbronn, Wurttemberg {Germany}], who is credited with discovering the mineral in 1774 at the Cape of Good Hope in South Africa. Von Prehn was a governor of Cape of Good Hope (1779-1780) until he was dismissed. He was a naturalist and mineral collector who brought the first specimens of his namesake mineral to Europe. It is unknown how the mineral came to the attention of Werner. A considerable mystique and folklore have surrounded Prehn and prehnite. The appellation "von" was supposedly bestowed on Prehn for his military service during the Seven Year's War, but there are no printed records available to substantiate the claim. It has been claimed that prehnite was the first mineral named for a person. In 1813, Richard Chenevix wrote a lengthy article (100+ pages) decrying the naming of minerals for people.)
A relatively common calcium alumosilicate occurring in low-temperature hydrothermal environments.
Colourless brick-shaped crystals may be confused with stellerite.

Visit gemdat.org for gemological information about Prehnite.


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Classification of PrehniteHide

Approved, 'Grandfathered' (first described prior to 1959)
9.DP.20

9 : SILICATES (Germanates)
D : Inosilicates
P : Transitional ino-phyllosilicate structures
72.1.3.1

72 : PHYLLOSILICATES Two-Dimensional Infinite Sheets with Other Than Six-Membered Rings
1 : Two-Dimensional Infinite Sheets with Other Than Six-Membered Rings with 4-membered rings
16.9.10

16 : Silicates Containing Aluminum and other Metals
9 : Aluminosilicates of Ca

Physical Properties of PrehniteHide

Vitreous, Pearly
Transparency:
Translucent
Comment:
Pearly on cleavage {001}
Colour:
Colourless to gray to yellow, yellow-green or white
Streak:
White
Hardness:
6 - 6½ on Mohs scale
Tenacity:
Brittle
Cleavage:
Distinct/Good
Good on {001}, poor on {110}
Fracture:
Irregular/Uneven
Density:
2.8 - 2.95 g/cm3 (Measured)    2.9 g/cm3 (Calculated)

Optical Data of PrehniteHide

Type:
Biaxial (+)
RI values:
nα = 1.611 - 1.632 nβ = 1.615 - 1.642 nγ = 1.632 - 1.665
2V:
Measured: 64° to 70°, Calculated: 58° to 68°
Max Birefringence:
δ = 0.021 - 0.033
Image shows birefringence interference colour range (at 30µm thickness)
and does not take into account mineral colouration.
Surface Relief:
Moderate
Dispersion:
weak r > v

Chemical Properties of PrehniteHide

Formula:
Ca2Al2Si3O10(OH)2
IMA Formula:
Ca2Al(Si3Al)O10(OH)2
Common Impurities:
Ti,Fe,Mg,Na,K,H2O

Crystallography of PrehniteHide

Crystal System:
Orthorhombic
Class (H-M):
mm2 - Pyramidal
Cell Parameters:
a = 4.646(2) Å, b = 5.491(3) Å, c = 18.52(3) Å
Ratio:
a:b:c = 0.846 : 1 : 3.373
Unit Cell V:
472.47 ų (Calculated from Unit Cell)
Z:
2
Morphology:
Uncommon crystals, aggregates are fanlike, reniform, globular, stalactitic, granular, compact.
Twinning:
Fine lamellar

X-Ray Powder DiffractionHide

Image Loading

Radiation - Copper Kα
Data Set:
Data courtesy of RRUFF project at University of Arizona, used with permission.
Powder Diffraction Data:
d-spacingIntensity
3.48 (90)
3.28 (60)
3.08 (100)
2.55 (100)
2.37 (40)
2.31 (40)
1.77 (70)
(

Type Occurrence of PrehniteHide

Synonyms of PrehniteHide

Other Language Names for PrehniteHide

Varieties of PrehniteHide

PatricianiteA pink variety of prehnite, commonly found in the basalts of the Keweenaw Peninsula, Michigan. It may contain intermixed chlorite and native copper inclusions, and can be confused with thomsonite.

Common AssociatesHide

Associated Minerals Based on Photo Data:
Epidote792 photos of Prehnite associated with Epidote on mindat.org.
Quartz698 photos of Prehnite associated with Quartz on mindat.org.
Calcite657 photos of Prehnite associated with Calcite on mindat.org.
Babingtonite335 photos of Prehnite associated with Babingtonite on mindat.org.
Laumontite172 photos of Prehnite associated with Laumontite on mindat.org.
Apophyllite157 photos of Prehnite associated with Apophyllite on mindat.org.
Copper148 photos of Prehnite associated with Copper on mindat.org.
Gyrolite114 photos of Prehnite associated with Gyrolite on mindat.org.
Hydroxyapophyllite-(K)88 photos of Prehnite associated with Hydroxyapophyllite-(K) on mindat.org.
Pectolite86 photos of Prehnite associated with Pectolite on mindat.org.

Related Minerals - Nickel-Strunz GroupingHide

9.DP.05Meliphanite(Ca,Na)2(Be,Al)[Si2O6(OH,F)]Tet. 4 : I4
9.DP.15LeucospheniteBaNa4Ti2B2Si10O30Mon.
9.DP.25AmstalliteCaAl(Si,Al)4O8(OH)4 · (H2O,Cl)Mon. 2/m : B2/b
9.DP.30KvanefjelditeNa4(Ca,Mn)(Si3O7)2(OH)2Orth.
9.DP.35Lemoynite(Na,K)2CaZr2Si10O26 · 5H2OMon. 2/m : B2/b
9.DP.35NatrolemoyniteNa4Zr2Si10O26•9H2OMon. 2/m : B2/m
9.DP.40AltisiteNa3K6Ti2Al2Si8O26Cl3Mon.

Related Minerals - Hey's Chemical Index of Minerals GroupingHide

16.9.1GehleniteCa2Al(AlSiO7)Tet. 4 2m : P4 21m
16.9.2AnorthiteCa(Al2Si2O8)Tric. 1 : P1
16.9.3Yoshiokaite(Ca,Na)[Al(Al,Si)O4]Trig. 3 : P3
16.9.4SvyatoslaviteCa(Al2Si2O8)Orth.
16.9.5DmisteinbergiteCa(Al2Si2O8)Hex. 6/mmm (6/m 2/m 2/m) : P6/mmm
16.9.6GrossularCa3Al2(SiO4)3Iso. m3m (4/m 3 2/m) : Ia3d
16.9.7VuagnatiteCaAl(SiO4)(OH)Orth.
16.9.8Zoisite{Ca2}{Al3}(Si2O7)(SiO4)O(OH)Orth. mmm (2/m 2/m 2/m) : Pnma
16.9.9Clinozoisite{Ca2}{Al3}(Si2O7)(SiO4)O(OH)Mon. 2/m : P21/m
16.9.11KamaishiliteCa2(Al2SiO6)(OH)2Tet.
16.9.12BicchuliteCa2(Al2SiO6)(OH)2Iso. 4 3m : I4 3m
16.9.13MargariteCaAl2(Al2Si2O10)(OH)2Mon.
16.9.14ChantaliteCaAl2(SiO4)(OH)4Tet. 4/m : I41/a
16.9.15CebolliteCa5Al2(SiO4)3(OH)4Orth.
16.9.17KatoiteCa3Al2(SiO4)3-x(OH)4xIso.
16.9.18LawsoniteCaAl2(Si2O7)(OH)2 · H2OOrth. mmm (2/m 2/m 2/m) : Cmcm
16.9.19ParthéiteCa2(Si4Al4) O15 (OH)2•4H2OMon. 2/m : B2/b
16.9.20WairakiteCa(Al2Si4O12) · 2H2OMon. 2/m
16.9.21VertumniteCa4Al4Si4O6(OH)24 · 3H2OMon. 2/m : P21/m
16.9.22ScoleciteCaAl2Si3O10 · 3H2OMon. m : Bb
16.9.23LaumontiteCaAl2Si4O12 · 4H2OMon. 2/m : B2/m
16.9.24YugawaraliteCaAl2Si6O16 · 4H2OMon.
16.9.25Gismondine-CaCaAl2Si2O8 · 4H2O
16.9.26EpistilbiteCaAl2Si6O16 · 5H2OMon.
16.9.27GoosecreekiteCa[Al2Si6O16] · 5H2OMon.
16.9.28CowlesiteCaAl2Si3O10 · 6H2OOrth.
16.9.30StelleriteCa4(Si28Al8)O72 · 28H2OOrth. mmm (2/m 2/m 2/m) : Fmmm
16.9.31SträtlingiteCa2Al2SiO7 · 8H2OTrig.
16.9.32AmstalliteCaAl(Si,Al)4O8(OH)4 · (H2O,Cl)Mon. 2/m : B2/b

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.

Prehnite in petrologyHide

Common component of (items highlighted in red)

References for PrehniteHide

Reference List:
Sort by Year (asc) | by Year (desc) | by Author (A-Z) | by Author (Z-A)
Aumento, F. (1968) The space group of prehnite. The Canadian Mineralogist: 9: 485-492.
Metcalf-Johansen, J. (1983) Prehnite from the Ilimaussaq alkaline intrusion. Mineralogical Magazine, vol. 47, n° 344, 403-404.
Akizuki, M. (1987) Al,Si order and the internal texture of prehnite. The Canadian Mineralogist: 25: 707.
Zunic, T.B., Scavnicar, S., Molin, G. (1990) Crystal structure of prehnite from Komiza. European Journal of Mineralogy: 2: 731-734.

Internet Links for PrehniteHide

Localities for PrehniteHide

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 ListShow