Prehnite
This page is currently not sponsored. Click here to sponsor this page.
Formula:
Ca2Al2Si3O10(OH)2
System:
Orthorhombic
Colour:
Colourless to gray to ...
Lustre:
Vitreous, Pearly
Hardness:
6 - 6½
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.
Colourless brick-shaped crystals may be confused with stellerite.
Visit gemdat.org for gemological information about Prehnite.
Classification of Prehnite
Approved, 'Grandfathered' (first described prior to 1959)
8/G.07-30
9.DP.20
9 : SILICATES (Germanates)
D : Inosilicates
P : Transitional ino-phyllosilicate structures
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
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
16 : Silicates Containing Aluminum and other Metals
9 : Aluminosilicates of Ca
Physical Properties of Prehnite
Vitreous, Pearly
Diaphaneity (Transparency):
Translucent
Comment:
Pearly on cleavage {001}
Colour:
Colourless to gray to yellow, yellow-green or white
Streak:
White
Hardness (Mohs):
6 - 6½
Tenacity:
Brittle
Cleavage:
Distinct/Good
Good on {001}, poor on {110}
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 Prehnite
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 Prehnite
Formula:
Ca2Al2Si3O10(OH)2
IMA Formula:
Ca2Al(Si3Al)O10(OH)2
Common Impurities:
Ti,Fe,Mg,Na,K,H2O
Crystallography of Prehnite
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 Volume:
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 Diffraction:
Image Loading
Radiation - Copper Kα
Data courtesy of RRUFF project at University of Arizona, used with permission.
X-Ray Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 3.48 | (90) |
| 3.28 | (60) |
| 3.08 | (100) |
| 2.55 | (100) |
| 2.37 | (40) |
| 2.31 | (40) |
| 1.77 | (70) |
| ( |
Occurrences of Prehnite
Type Occurrence of Prehnite
Relationship of Prehnite to other Species
| 9.DP.05 | Meliphanite | (Ca,Na)2(Be,Al)[Si2O6(OH,F)] |
| 9.DP.15 | Leucosphenite | BaNa4Ti2B2Si10O30 |
| 9.DP.25 | Amstallite | CaAl(Si,Al)4O8(OH)4 · (H2O,Cl) |
| 9.DP.30 | Kvanefjeldite | Na4(Ca,Mn)(Si3O7)2(OH)2 |
| 9.DP.35 | Lemoynite | (Na,K)2CaZr2Si10O26 · 5H2O |
| 9.DP.35 | Natrolemoynite | Na4Zr2Si10O26•9H2O |
| 9.DP.40 | Altisite | Na3K6Ti2Al2Si8O26Cl3 |
| 16.9.1 | Gehlenite | Ca2Al(AlSiO7) |
| 16.9.2 | Anorthite | Ca(Al2Si2O8) |
| 16.9.3 | Yoshiokaite | (Ca,Na)[Al(Al,Si)O4] |
| 16.9.4 | Svyatoslavite | Ca(Al2Si2O8) |
| 16.9.5 | Dmisteinbergite | Ca(Al2Si2O8) |
| 16.9.6 | Grossular | Ca3Al2(SiO4)3 |
| 16.9.7 | Vuagnatite | CaAl(SiO4)(OH) |
| 16.9.8 | Zoisite | {Ca2}{Al3}(Si2O7)(SiO4)O(OH) |
| 16.9.9 | Clinozoisite | {Ca2}{Al3}(Si2O7)(SiO4)O(OH) |
| 16.9.11 | Kamaishilite | Ca2(Al2SiO6)(OH)2 |
| 16.9.12 | Bicchulite | Ca2(Al2SiO6)(OH)2 |
| 16.9.13 | Margarite | CaAl2(Al2Si2O10)(OH)2 |
| 16.9.14 | Chantalite | CaAl2(SiO4)(OH)4 |
| 16.9.15 | Cebollite | Ca5Al2(SiO4)3(OH)4 |
| 16.9.17 | Katoite | Ca3Al2(SiO4)3-x(OH)4x |
| 16.9.18 | Lawsonite | CaAl2(Si2O7)(OH)2 · H2O |
| 16.9.19 | Parthéite | Ca2(Si4Al4) O15 (OH)2•4H2O |
| 16.9.20 | Wairakite | Ca(Al2Si4O12) · 2H2O |
| 16.9.21 | Vertumnite | Ca4Al4Si4O6(OH)24 · 3H2O |
| 16.9.22 | Scolecite | CaAl2Si3O10 · 3H2O |
| 16.9.23 | Laumontite | CaAl2Si4O12 · 4H2O |
| 16.9.24 | Yugawaralite | CaAl2Si6O16 · 4H2O |
| 16.9.25 | Gismondine-Ca | CaAl2Si2O8 · 4H2O |
| 16.9.26 | Epistilbite | CaAl2Si6O16 · 5H2O |
| 16.9.27 | Goosecreekite | Ca[Al2Si6O16] · 5H2O |
| 16.9.28 | Cowlesite | CaAl2Si3O10 · 6H2O |
| 16.9.30 | Stellerite | Ca4(Si28Al8)O72 · 28H2O |
| 16.9.31 | Strätlingite | Ca2Al2SiO7 · 8H2O |
| 16.9.32 | Amstallite | CaAl(Si,Al)4O8(OH)4 · (H2O,Cl) |
Other Names for Prehnite
Name in Other Languages:
Other Information
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 petrology
Common component of (items highlighted in red)
References for Prehnite
Reference List:
Aumento, F. (1968) The space group of prehnite. The Canadian Mineralogist: 9: 485-492.
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.
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 Prehnite
mindat.org URL:
https://www.mindat.org/min-3277.html
Please feel free to link to this page.
Please feel free to link to this page.
Search Engines:
External Links:
Mineral Dealers:
Specimens:
The following Prehnite specimens are currently listed for sale on minfind.com.
La Combe de la Selle, St Christophe-en-Oisans, Bourg d'Oisans, Isère, Auvergne-Rhône-Alpes, France