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Guanacoite

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Big Photo

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

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Formula:
Cu
 
2
Mg
 
3
(AsO
 
4
)
 
2
(OH)
 
4
 · 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)
2.215 (18)
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
 
3
(AsO
 
4
)
 
2
(OH)
 
4
 · 4H
 
2
O
Essential elements:As, Cu, H, Mg, 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
(AsO
 
4
)
 
2
(OH)
 
4
8.DD.05Luetheite
Cu
 
2
Al
 
2
(AsO
 
4
)
 
2
(OH)
 
4
8.DD.10Akrochordite
(Mn
2+
 
,Mg)
 
5
(AsO
 
4
)
 
2
(OH)
 
4
 · 4H
 
2
O
8.DD.15Aheylite
(Fe
2+
 
,Zn)Al
 
6
(PO
 
4
)
 
4
(OH)
 
8
 · 4H
 
2
O
8.DD.15Chalcosiderite
Cu(Fe
3+
 
,Al)
 
6
(PO
 
4
)
 
4
(OH)
 
8
 · 4H
 
2
O
8.DD.15Faustite
(Zn,Cu)Al
 
6
(PO
 
4
)
 
4
(OH)
 
8
 · 4H
 
2
O
8.DD.15Planerite
Al
 
6
(PO
 
4
)
 
2
(HPO
 
4
)
 
2
(OH)
 
8
 · 4 H
 
2
O
8.DD.15Turquoise
Cu(Al,Fe
3+
 
)
 
6
(PO
 
4
)
 
4
(OH)
 
8
 · 4H
 
2
O
8.DD.15Afmite
Al
 
3
(OH)
 
4
(H2O)
 
3
(PO
 
4
)(PO
 
3
OH) · H2O
8.DD.20Childrenite
(Fe
2+
 
,Mn
2+
 
)Al(PO
 
4
)(OH)
 
2
 · H
 
2
O
8.DD.20Eosphorite
(Mn
2+
 
,Fe
2+
 
)Al(PO
 
4
)(OH)
 
2
 · H
 
2
O
8.DD.20Ernstite
(Mn
2+
 
,Fe
3+
 
)Al(PO
 
4
)(OH,O)
 
2
 · 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.

Internet Links for Guanacoite

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    • Localities for Guanacoite

    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.
    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 Azer District (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.
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