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Guanacoite

Big Photo

El Guanaco Mine, Guanaco (Huanaco), Santa Catalina, Antofagasta Province, Antofagasta Region, Chile
© Brent Thorne

Show Guanacoite Photos (27)
Formula:
Cu
 
2
Mg
 
2
(Mg
 
0.5
Cu
 
0.5
)[(OH)
 
2
|AsO
 
4
]
 
2
 · 4H
 
2
O
System:MonoclinicColour:Blue to pale blue
Hardness:3
Name:For the type locality.


A rare secondary Cu-Mg arsenate, isotypic with Akrochordite.

The Cu:Mg ratios on the three Cu/Mg sites in the crystal structure were shown to be variable and a Mg-dominant member has been reported by Kyono (2008), but not proposed as a new mineral species yet.

Classification of Guanacoite

IMA status:Approved 2003
Strunz 8th edition ID:7/D.16-25
Strunz 9th edition ID:8.DD.10
Nickel-Strunz 10th (pending) edition ID:8.DD.10

8 : PHOSPHATES, ARSENATES, VANADATES
D : Phosphates, etc. with additional anions, with H2O
D : With only medium-sized cations, (OH, etc.):RO4= 2:1
Dana 8th edition ID:42.4.1.2

42 : HYDRATED PHOSPHATES, ETC.CONTAINING HYDROXYL OR HALOGEN
4 : (AB)5(XO4)2Zq·xH2O
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Type Occurrence of Guanacoite

Type Locality:El Guanaco Mine, Guanaco (Huanaco), Santa Catalina, Antofagasta Province, Antofagasta Region, Chile
General Appearance of Type Material:Prismatic to acicular crystals up to 0.7 mm in length
Associated Minerals at type locality:
QuartzOliveniteEnargiteConichalciteChrysocolla
BrochantiteArhbarite

Physical Properties of Guanacoite

Lustre:Vitreous
Diaphaneity (Transparency):Transparent
Colour:Blue to pale blue
Streak:White to pale blue
Hardness (Mohs):3
Hardness Data:Estimated
Tenacity:Brittle
Cleavage:Distinct/Good
Parallel to {010}
Fracture:Irregular/Uneven, Conchoidal
Density (measured):3.31 g/cm3
Density (calculated):3.36 g/cm3
Comment:The calculated density refers to the ideal composition; the average Cu/Mg ratio measured by microprobe leads to a density of 3.30 g/cm3

Crystallography of Guanacoite

Crystal System:Monoclinic
Class (H-M):2/m - Prismatic
Space Group:P21/b {P1 1 21/b} {P21/c} {P1 21/c 1} {P21/a}
Cell Parameters:a = 5.475(1) Å, b = 16.865(3) Å, c = 6.915(1) Å
β = 99.8(3)°
Ratio:a:b:c = 0.325 : 1 : 0.41
Unit Cell Volume:V 629.2 ų
Z:2
Morphology:Prismatic along [100].
Twinning:None observed.
Comment:Cell parameters from single-crystal data
X-Ray Powder Diffraction:
d-spacingIntensity
8.421 (100)
5.399 (38)
5.141 (17)
4.473 (17)
4.331 (38)
4.211 (24)
3.403 (21)
3.081 (28)
3.019 (18)
2.910 (35)
2.737 (35)
2.677 (25)
2.666 (19)
2.281 (23)
Comments:Calculated data (measured data show preferred orientation due to cleavage).

Optical Data of Guanacoite

Type:Biaxial (-)
RI values: nα = 1.664(1) nβ = 1.691(1) nγ = 1.695(1)
2V:Measured: 31° , Calculated: 42°
Maximum Birefringence:δ = 0.031

Chart shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:High
Dispersion:r > v, weak
Pleochroism:Non-pleochroic
Comments:Oientation: X ∼ c, Y vs. a = 10° (in obtuse β), Z = b

Chemical Properties of Guanacoite

Formula:
Cu
 
2
Mg
 
2
(Mg
 
0.5
Cu
 
0.5
)[(OH)
 
2
|AsO
 
4
]
 
2
 · 4H
 
2
O
All elements listed in formula:As, Cu, H, Mg, O
Analytical Data:Results from electron microprobe analysis, except for water (by thermal analysis)
CuO    (29.67)
MgO    (17.12)
As2O5  (35.67)
H2O    (18)

total  100.46 wt.-%
Empirical Formula:
Cu
 
2.32
Mg
 
2.64
(OH)
 
4.13
(H
 
2
O)
 
4.15
(AsO
 
4
)
 
1.93

Relationship of Guanacoite to other Species

Related Minerals - Nickel-Strunz Grouping):

- +
8.DD.05Chenevixite
Cu
 
2
Fe
3+
2
[(OH)
 
2
|AsO
 
4
]
 
2
8.DD.05Luetheite
Cu
 
2
Al
 
2
[(OH)
 
2
|AsO
 
4
]
 
2
8.DD.10Akrochordite
(Mn
2+
 
,Mg)
 
5
[(OH)
 
2
|AsO
 
4
]
 
2
 · 4H
 
2
O
8.DD.15Aheylite
(Fe
2+
 
,Zn)Al
 
6
[(OH)
 
4
|(PO
 
4
)
 
2
]
 
2
 · 4H
 
2
O
8.DD.15Chalcosiderite
Cu(Fe
3+
 
,Al)
 
6
[(OH)
 
4
|(PO
 
4
)
 
2
]
 
2
 · 4H
 
2
O
8.DD.15Faustite
(Zn,Cu)Al
 
6
[(OH)
 
4
|(PO
 
4
)
 
2
]
 
2
 · 4H
 
2
O
8.DD.15Planerite
Al
 
6
[(OH)
 
4
|HPO
 
4
|PO
 
4
]
 
2
 · 4 H
 
2
O
8.DD.15Turquoise
Cu(Al,Fe
3+
 
)
 
6
[(OH)
 
4
|(PO
 
4
)
 
2
]
 
2
 · 4H
 
2
O
8.DD.20Childrenite
(Fe
2+
 
,Mn
2+
 
)Al[(OH)
 
2
|PO
 
4
] · H
 
2
O
8.DD.20Eosphorite
(Mn
2+
 
,Fe
2+
 
)Al[(OH)
 
2
|PO
 
4
] · H
 
2
O
8.DD.20Ernstite
(Mn
2+
 
,Fe
3+
 
)Al[(OH,O)
 
2
|PO
 
4
] · H
 
2
O

Other Names for Guanacoite

Synonyms:
IMA2003-021
Other Languages:
German:Guanacoit
Spanish:Guanacoita

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 Guanacoite

Reference List:Witzke, T., Kolitsch, U., Krause, W., Wiechowski, A., Medenbach, O., Kampf, A.R., Steele, I.M., Favreau, G. (2006): Guanacoite, Cu2Mg2(Mg0.5Cu0.5)(OH)4(H2O)4(AsO4)2, a new arsenate mineral species from the El Guanaco Mine, near Taltal, Chile: Description and crystal structure. European Journal of Mineralogy, 18, 813-821.

Kyono, A. (2008): Compositional variability and crystal structural features of guanacoite. American Mineralogist: 93: 501-507.

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    Localities for Guanacoite

    (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.
    Chile
     
    • Antofagasta Region
      • Antofagasta Province
        • Santa Catalina
          • Guanaco (Huanaco)
    		Witzke, T., Kolitsch, U., Krause, W., Wiechowski, A., Medenbach, O., Kampf, A.R., Steele, I.M., Favreau, G. (2006): Guanacoite, Cu2Mg2(Mg0.5Cu0.5)(OH)4(H2O)4(AsO4)2, a new arsenate mineral species from the El Guanaco Mine, near Taltal, Chile: Description and crystal structure. European Journal of Mineralogy, 18, 813-821.
    Morocco
     
    • Souss-Massa-Draâ Region
      • Ouarzazate Province
        • Tazenakht
          • Bou Azzer District
            • Taghouni
    		T. Witzke, U. Kolitsch, W. Krause, A. Wiechowski, O. Medenbach, A. R. Kampf, I. M. Steele and G. Favreau (2006): Guanacoite, Cu2Mg2(Mg0.5Cu0.5)(OH)4(H2O)4(AsO4)2, a new arsenate mineral species from the El Guanaco Mine, near Taltal, Chile: Description and crystal structure. Eur. J. Mineral. 18, 813-821.
    Mineral and/or Locality
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