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Congolite

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Formula:
(Fe
2+
 
,Mg)
 
3
(B
 
7
O
 
13
)Cl
System:TrigonalHardness:6½ - 7½
Member of:Boracite Group
Dimorph of:Ericaite


Boracite Group. The Fe2+ analogue of Trembathite. The trigonal dimorph of Ericaite.

Classification of Congolite

IMA status:Approved
Strunz 8th edition ID:5/L.04-40
Nickel-Strunz 10th (pending) edition ID:6.GA.10

6 : BORATES
G : Heptaborates and other megaborates
A : Tekto-heptaborates
Dana 8th edition ID:25.6.2.1

25 : ANHYDROUS BORATES CONTAINING HYDROXYL OR HALOGEN
6 : Hexaborates
Hey's CIM Ref.:10.1.19

10 : Borates with other anions
1 : Borates with halide
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Type Occurrence of Congolite

Type Locality:Kouilou Department, Republic of Congo (Brazzaville)
Year of Discovery:1972

Physical Properties of Congolite

Hardness (Mohs):6½ - 7½

Crystallography of Congolite

Crystal System:Trigonal
Cell Parameters:a = 8.62Å, c = 21.05Å
Ratio:a:c = 1 : 2.442
Unit Cell Volume:V 1,354.56 ų (Calculated from Unit Cell)

Optical Data of Congolite

Type:Uniaxial (-)
RI values: nω = 1.755 nε = 1.731
Maximum Birefringence:δ = 0.024

Chart shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:High

Chemical Properties of Congolite

Formula:
(Fe
2+
 
,Mg)
 
3
(B
 
7
O
 
13
)Cl
Simplified for copy/paste:(Fe2+,Mg)3(B7O13)Cl
Essential elements:B, Cl, Fe, O
All elements listed in formula:B, Cl, Fe, Mg, O

Relationship of Congolite to other Species

Member of:Boracite Group
Other Members of Group:

- +
Boracite
Mg
 
3
(B
 
7
O
 
13
)Cl
Chambersite
Mn
2+
3
(B
 
7
O
 
13
)Cl
Ericaite
Fe
2+
3
(B
 
7
O
 
13
)Cl
Trembathite
(Mg,Fe)
 
3
(B
 
7
O
 
13
)Cl
Related Minerals - Nickel-Strunz Grouping):

- +
6.GA.05Boracite
Mg
 
3
(B
 
7
O
 
13
)Cl
6.GA.05Chambersite
Mn
2+
3
(B
 
7
O
 
13
)Cl
6.GA.05Ericaite
Fe
2+
3
(B
 
7
O
 
13
)Cl
6.GA.10Trembathite
(Mg,Fe)
 
3
(B
 
7
O
 
13
)Cl
6.GA.30Korzhinskite
Ca(B
 
2
O
 
4
) · H
 
2
O
Related Minerals - Hey's Index Grouping:

- +
10.1.1Teepleite
Na
 
2
[B(OH)
 
4
]Cl
10.1.2Bandylite
Cu[B(OH)
 
4
]Cl
10.1.3Berborite
Be
 
2
(BO
 
3
)(OH,F) · H
 
2
O
10.1.4Fluoborite
Mg
 
3
(BO
 
3
)(F,OH)
 
3
10.1.5Boracite
Mg
 
3
(B
 
7
O
 
13
)Cl
10.1.6Karlite
Mg
 
7
(BO
 
3
)
 
3
(OH,Cl)
 
5
10.1.7Shabynite
Mg
 
5
(BO
 
3
)(OH)
 
5
(Cl,OH)
 
2
· 4H
 
2
O
10.1.8/9/10Hilgardite
Ca
 
2
B
 
5
O
 
9
Cl · H
 
2
O
10.1.11Solongoite
Ca
 
2
(H
 
3
B
 
3
O
 
7
)(OH)Cl
10.1.12Hydrochlorborite
Ca
 
4
B
 
8
O
 
15
Cl
 
2
· 21H
 
2
O
10.1.13Ekaterinite
Ca
 
2
(B
 
4
O
 
7
)(Cl,OH)
 
2
· 2H
 
2
O
10.1.14Volkovskite
KCa
 
4
[B
 
5
O
 
8
OH]
 
4
[B(OH)
 
3
]
 
2
Cl · 4H
 
2
O
10.1.15Chelkarite
CaMgB
 
2
O
 
4
(Cl,OH)
 
2
· 5H
 
2
O Or near, with Cl:OH = 3:1
10.1.16Johachidolite
CaAlB
 
3
O
 
7
10.1.17Satimolite
KNa
 
2
Al
 
4
[Cl|B
 
2
O
 
5
]
 
3
· 13H
 
2
O
10.1.18Chambersite
Mn
2+
3
(B
 
7
O
 
13
)Cl
10.1.20Ericaite
Fe
2+
3
(B
 
7
O
 
13
)Cl

Other Names for Congolite

Synonyms:
IMA1971-030
Other Languages:
German:Congolit
Russian:Конголит
Spanish:Congolita

Other Information

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 Congolite

Reference List:

- +
American Mineralogist (1972): 57: 1315.

Zeitschrift für Kristallographie: 138: 64-99.

Burns, P.C. and Carpenter, M.A. (1996) Phase transitions in the series boracite-trembathite-congolite: phase relations. Canadian Mineralogist: 34: 881-892.

Grew, E.S., and Anovitz, L.M. (1996) BORON: Mineralogy, Petrology and Geochemistry, second edition, as revised (2002).

Internet Links for Congolite

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

    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.
    Canada
     
    • New Brunswick
      • Kings Co.
        • Cardwell Parish
    CM 43, 1469-1487
    Grice, J. L. (2002): Borate Minerals from the Penobsquis and Millstream Deposits of Southern New Brunswick, Canada. Bergverksmuseets Skrift 20, 27-33
        • Studholm Parish
    Canadian Mineralogist: 43: 1469-1487.
    Poland
     
    • Wielkopolskie
    PIECZKA, A. & WACHOWIAK, J. (2012) CONGOLITE FROM THE KŁODAWA SALT MINE (CENTRAL POLAND) AND ITS IMPORTANCE AT EVALUATION OF METAMORPHIC CONDITIONS IN THE SALT DOME. Acta Mineralogica-Petrographica, Abstract Series, Szeged, Vol. 7, 2012 , 107. [http://www.mineral.hermuz.hu/acta_07/pdf/107-Pieczka.pdf]
    Republic of Congo (Brazzaville)
     
    • Brazzaville Department
    American Mineralogist (1972): 57: 1315.
    American Mineralogist (1972): 57: 1315.
    UK
     
    • England
      • North Yorkshire
        • Loftus
    Bart Cannon analyses
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