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Bentorite

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Hatrurim Formation, Negev, Israel
© 2008 Jesse Crawford

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Formula:
Ca
 
6
(Cr
3+
 
,Al)
 
2
(SO
 
4
)
 
3
(OH)
 
12
 · 26H
 
2
O
System:HexagonalColour:Violet to rose-purple
Lustre:Resinous, Waxy, EarthyHardness:2
Member of:Ettringite Group
Name:Named in 1977 by Shulamit Gross in honor of Professor Yaakov K. Ben-Tor [February 13, 1910 Königsberg, East Prussia, Germany - October 29, 2002 La Jolla, California, USA], petrologist and geologist, Scripps Institute of Oceanography, University of California, San Diego, California, USA and Department head of Geology, Hebrew University, Jerusalem, Israel from 1954-1966, for his contributions to the geology and mineralogy of Israel and the Middle East.


Ettringite Group.
The Cr(III) analogue of ettringite.

Not to be confused with bentonite

Classification of Bentorite

IMA status:Approved 1979
Strunz 8th edition ID:6/D.13-20
Strunz 9th edition ID:7.DG.15
Nickel-Strunz 10th (pending) edition ID:7.DG.15

7 : SULFATES (selenates, tellurates, chromates, molybdates, wolframates)
D : Sulfates (selenates, etc.) with additional anions, with H2O
G : With large and medium-sized cations; with NO3, CO3, B(OH)4, SiO4 or IO3
Dana 8th edition ID:31.10.2.2

31 : HYDRATED SULFATES CONTAINING HYDROXYL OR HALOGEN
10 : Miscellaneous
Hey's CIM Ref.:25.4.14

25 : Sulphates
4 : Sulphates of Ca, Sr and Ba
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Type Occurrence of Bentorite

Type Locality:Hatrurim Formation, Negev, Israel
General Appearance of Type Material:Fine-grained deep purple to light rosey purple masses and veinlet filling.
Year of Discovery:1975
Geological Setting of type material:Auto-metamorphosed marble: Hatrurim Formation
Associated Minerals at type locality:
SpurriteMayeniteCalciteBrownmillerite

Physical Properties of Bentorite

Lustre:Resinous, Waxy, Earthy
Diaphaneity (Transparency):Transparent
Comment:Originally said to be vitreous
Colour:Violet to rose-purple
Streak:Very pale purple
Hardness (Mohs):2
Cleavage:Perfect
{10-0} perfect; {0001} good
Fracture:Sub-Conchoidal
Density (measured):2.025 g/cm3
Density (calculated):2.021 g/cm3

Crystallography of Bentorite

Crystal System:Hexagonal
Class (H-M):6/mmm (6/m 2/m 2/m) - Dihexagonal Dipyramidal
Space Group:P63/mmc {P63/m 2/m 2/c}
Space Group Setting:P63/mmc
Cell Parameters:a = 22.35Å, c = 21.41Å
Ratio:a:c = 1 : 0.958
Unit Cell Volume:V 9,261.95 ų (Calculated from Unit Cell)
Z:8
Morphology:Euhedral crystals very rare. Minute crystals (<< 1 mm) show first- and second-order prisms.
Twinning:{10-10}
X-Ray Powder Diffraction:
Image Loading

Radiation - Copper Kα
Data Set:
Horizontal Axis: ° to ° Vertical Axis: % Source Data: Filtered Data:
Data courtesy of RRUFF project at University of Arizona, used with permission.
X-Ray Powder Diffraction:
d-spacingIntensity
9.66 (100)
5.59 (40)
3.89 (10)
3.60 (10)
3.23 (10)
2.77 (10)
2.21 (10)
1.94 (20)
Comments:ICDD 33-248

Optical Data of Bentorite

Type:Uniaxial (+)
RI values: nω = 1.478 nε = 1.484
Birefringence:0.006
Maximum Birefringence:δ = 0.006

Chart shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:Moderate
Optical Extinction:Parallel
Pleochroism:Visible
Comments:O = colorless; E = pale violet purple
Comments:Absorption E > O

Chemical Properties of Bentorite

Formula:
Ca
 
6
(Cr
3+
 
,Al)
 
2
(SO
 
4
)
 
3
(OH)
 
12
 · 26H
 
2
O
Essential elements:Ca, Cr, H, O, S
All elements listed in formula:Al, Ca, Cr, H, O, S

Relationship of Bentorite to other Species

Member of:Ettringite Group
Other Members of Group:

- +
Buryatite
Ca
 
3
(Si,Fe,Al)(SO
 
4
)[B(OH)
 
4
]O(OH)
 
5
 · 12H
 
2
O
Carraraite
Ca
 
3
(SO
 
4
)[Ge(OH)
 
6
](CO
 
3
) · 12H
 
2
O
Charlesite
Ca
 
6
(Al,Si)
 
2
(SO
 
4
)
 
2
[B(OH)
 
4
](OH,O)
 
12
 · 26H
 
2
O
Ettringite
Ca
 
6
Al
 
2
(SO
 
4
)
 
3
(OH)
 
12
 · 26H
 
2
O
Jouravskite
Ca
 
6
Mn
3+
2
(SO
 
4
,CO
 
3
)
 
3
(OH)
 
12
 · 26H
 
2
O
Micheelsenite
(Ca,Y)
 
3
Al(HPO
 
4
,CO
 
3
)(CO
 
3
)(OH)
 
6
 · 12H
 
2
O
Sturmanite
Ca
 
6
(Fe
3+
 
,Al,Mn
3+
 
)
 
2
(SO
 
4
)
 
2
[B(OH)
 
4
](OH)
 
12
 · 25H
 
2
O
Thaumasite
Ca
 
3
(SO
 
4
)[Si(OH)
 
6
](CO
 
3
) · 12H
 
2
O
Related Minerals - Nickel-Strunz Grouping):

- +
7.DG.05Darapskite
Na
 
3
(SO
 
4
)(NO
 
3
) · H
 
2
O
7.DG.10Clinoungemachite
(Na, K, Fe, SO
 
4
)
7.DG.10Humberstonite
Na
 
7
K
 
3
Mg
 
2
(SO
 
4
)
 
6
(NO
 
3
)
 
2
 · 6H
 
2
O
7.DG.10Ungemachite
K
 
3
Na
 
8
Fe(SO
 
4
)
 
6
(NO
 
3
)
 
2
 · 6H
 
2
O
7.DG.15Charlesite
Ca
 
6
(Al,Si)
 
2
(SO
 
4
)
 
2
[B(OH)
 
4
](OH,O)
 
12
 · 26H
 
2
O
7.DG.15Ettringite
Ca
 
6
Al
 
2
(SO
 
4
)
 
3
(OH)
 
12
 · 26H
 
2
O
7.DG.15Jouravskite
Ca
 
6
Mn
3+
2
(SO
 
4
,CO
 
3
)
 
3
(OH)
 
12
 · 26H
 
2
O
7.DG.15Sturmanite
Ca
 
6
(Fe
3+
 
,Al,Mn
3+
 
)
 
2
(SO
 
4
)
 
2
[B(OH)
 
4
](OH)
 
12
 · 25H
 
2
O
7.DG.15Thaumasite
Ca
 
3
(SO
 
4
)[Si(OH)
 
6
](CO
 
3
) · 12H
 
2
O
7.DG.15Carraraite
Ca
 
3
(SO
 
4
)[Ge(OH)
 
6
](CO
 
3
) · 12H
 
2
O
7.DG.15Buryatite
Ca
 
3
(Si,Fe,Al)(SO
 
4
)[B(OH)
 
4
]O(OH)
 
5
 · 12H
 
2
O
7.DG.20Rapidcreekite
Ca
 
2
(SO
 
4
)(CO
 
3
) · 4H
 
2
O
7.DG.20Korkinoite
Ca
 
4
(SO
 
4
)
 
2
(CO
 
3
)
 
2
 · 9(H
 
2
O)
7.DG.25Tatarskite
Ca
 
6
Mg
 
2
(SO
 
4
)
 
2
(CO
 
3
)
 
2
(OH)
 
4
Cl
 
4
 · 7H
 
2
O
7.DG.30Nakauriite
Cu
 
8
(SO
 
4
)
 
4
(CO
 
3
)(OH)
 
6
 · 48H
 
2
O
7.DG.35Chessexite
(Na,K)
 
4
Ca
 
2
(Mg,Zn)
 
3
Al
 
8
(SO
 
4
)
 
10
(SiO
 
4
)
 
2
 · 40H
 
2
O
7.DG.40Carlosruizite
K
 
6
(Na,K)
 
4
Na
 
6
Mg
 
10
(SeO
 
4
)
 
12
(IO
 
3
)
 
12
 · 12H
 
2
O
7.DG.40Fuenzalidaite
K
 
6
(Na,K)
 
4
Na
 
6
Mg
 
10
(SO
 
4
)
 
12
(IO
 
3
)
 
12
 · 12H
 
2
O
7.DG.45Chelyabinskite
(Ca,Mg)
 
3
(SO
 
4
,CO
 
3
)
 
2
[Si(OH)
 
6
] · 9H
 
2
O (?)
Related Minerals - Hey's Index Grouping:

- +
25.4.1Anhydrite
CaSO
 
4
25.4.2Bassanite
CaSO
 
4
 · 0.5H
 
2
O
25.4.3Gypsum
CaSO
 
4
 · 2H
 
2
O
25.4.4Glauberite
Na
 
2
Ca(SO
 
4
)
 
2
25.4.5Cesanite
Na
 
3
Ca
 
2
(SO
 
4
)
 
3
(OH)
25.4.6Eugsterite
Na
 
4
Ca(SO
 
4
)
 
3
 · 2H
 
2
O
25.4.7Hydroglauberite
Na
 
10
Ca
 
3
(SO
 
4
)
 
8
 · 6H
 
2
O
25.4.8Syngenite
K
 
2
Ca(SO
 
4
)
 
2
 · H
 
2
O
25.4.9Görgeyite
K
 
2
Ca
 
5
(SO
 
4
)
 
6
 · H
 
2
O
25.4.10Polyhalite
K
 
2
Ca
 
2
Mg(SO
 
4
)
 
4
 · 2H
 
2
O
25.4.11Koktaite
(NH
 
4
)
 
2
Ca(SO
 
4
)
 
2
 · H
 
2
O
25.4.12Ye'elimite
Ca
 
4
Al
 
6
(SO
 
4
)O
 
12
25.4.13Ettringite
Ca
 
6
Al
 
2
(SO
 
4
)
 
3
(OH)
 
12
 · 26H
 
2
O
25.4.15Celestine
SrSO
 
4
25.4.16Kalistrontite
K
 
2
Sr(SO
 
4
)
 
2
25.4.17Baryte
BaSO
 
4

Other Names for Bentorite

Synonyms:
IMA1979-042
Other Languages:
German:Bentorit
Spanish:Bentorita

Other Information

Fluorescence in UV light:Not fluorescent
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 Bentorite

Reference List:

- +
Gross, S. (1980) Bentorite. A new mineral from the Hatrurim Area, west of the Dead Sea, Israel. Israel J. of Earth Sci., 29, 81–84. [abstract in Amer. Mineral., 66 (1981), 639]

Internet Links for Bentorite

Search Engines:
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  • Raman and XRD data at RRUFF project
  • American Mineralogist Crystal Structure Database
  • Bentorite details from Handbook of Mineralogy (PDF)
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    • Localities for Bentorite

    Hide Locality List
    (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.
    Israel
     
    • Negev
    		Gross, S. (1977): The Mineralogy of the Hatrurim Formation, Israel. Geological Survey of Israel, Bulletin no. 70, 80 pp.
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