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Lópezite

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Oficina Maria Elena, Tocopilla Province, Antofagasta Region, Chile
© 2004 JBS

Formula:
K
 
2
[Cr
 
2
O
 
7
]
System:TriclinicColour:Orange-red, red
Lustre:VitreousHardness:2½
Name:For Emiliano López Saa (1871-1959), Chilean mining engineer and mineral collector associated with the Chilean nitrate mining industry.


Note: Most commercially offered "lopezite" is in fact synthetic K2Cr2O7.

Classification of Lópezite

IMA status:Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
Strunz 8th edition ID:6/F.05-10
Nickel-Strunz 10th (pending) edition ID:7.FD.05

7 : SULFATES (selenates, tellurates, chromates, molybdates, wolframates)
F : Chromates
D : Dichromates
Dana 7th edition ID:35.2.1.1
Dana 8th edition ID:35.2.1.1

35 : ANHYDROUS CHROMATES
2 : A2X2O7
Hey's CIM Ref.:27.2.2

27 : Sulphites, Chromates, Molybdates and Tungstates
2 : Chromates
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Type Occurrence of Lópezite

Type Locality:Huara, Iquique Province, Tarapacá Region, Chile
General Appearance of Type Material:ball-like aggregates, to 1 mm.
Place of Conservation of Type Material:National Museum of Natural History, Washington, DC, USA C5487
Year of Discovery:1937
Geological Setting of type material:nitrate rock
Associated Minerals at type locality:
UlexiteTarapacáiteDietzeite

Physical Properties of Lópezite

Lustre:Vitreous
Diaphaneity (Transparency):Transparent
Colour:Orange-red, red
Streak:light yellow
Hardness (Mohs):2½
Cleavage:Perfect
[010] perfect, [100] distinct, [001] distinct
Density (measured):2.69 g/cm3
Density (calculated):2.704 g/cm3

Crystallography of Lópezite

Crystal System:Triclinic
Class (H-M):1 - Pinacoidal
Space Group:P1
Cell Parameters:a = 7.46Å, b = 13.4Å, c = 7.38Å
α = 90.75°, β = 96.21°, γ = 97.96°
Ratio:a:b:c = 0.557 : 1 : 0.551
Unit Cell Volume:V 722.41 ų
Z:4
Morphology:Ball-like aggregates (~ 1 mm diameter). Artificial crystals are short prismatic [001].
Twinning:Observed on artificial crystals.
X-Ray Powder Diffraction:
d-spacingIntensity
4.87 (45)
3.658 (85)
3.472 (80)
3.298 (100)
3.063 (30)
3.027 (30)
Comments:synthetic (ICDD 27-0380)

Optical Data of Lópezite

Type:Biaxial (+)
RI values: nα = 1.714 nβ = 1.732 nγ = 1.805
2V:Measured: 50° , Calculated: 56°
Maximum Birefringence:δ = 0.091

Chart shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:High
Dispersion:r > v, medium
Pleochroism:Visible
Comments:X = reddish yellow
Y = yellow
Z = greenish yellow

Chemical Properties of Lópezite

Formula:
K
 
2
[Cr
 
2
O
 
7
]
Essential elements:Cr, K, O
All elements listed in formula:Cr, K, O
Empirical Formula:
K
 
2
[Cr
6+
2
O
 
7
]

Relationship of Lópezite to other Species

Related Minerals - Hey's Index Grouping:

- +
27.2.1Tarapacáite
K
 
2
[CrO
 
4
]
27.2.3Chromatite
Ca[CrO
 
4
]
27.2.4Hashemite
Ba(Cr,S)O
 
4
27.2.5Crocoite
Pb(CrO
 
4
)
27.2.6Phoenicochroite
Pb
 
2
[O|CrO
 
4
]
27.2.7Santanaite
Pb
 
11
[O
 
12
|CrO
 
4
]
27.2.8Iranite
Pb
 
10
Cu[(F,OH)
 
2
|(CrO
 
4
)
 
6
|(SiO
 
4
)
 
2
]
27.2.9Hemihedrite
Pb
 
10
Zn[(F,OH)
 
2
|(CrO
 
4
)
 
6
|(SiO
 
4
)
 
2
]

Other Names for Lópezite

Other Languages:
German:Lopezit
Russian:Лопецит
Spanish:Lopezita

Other Information

Other Information:Readily soluble in water.
Health Warning:Chromate minerals contain the carcinogenic and mutagenic chromate ion. Always wash hands after handling. Avoid inhaling dust when handling or breaking. Never lick or ingest. Do not pour chromate-containing solutions down the drain.

References for Lópezite

Reference List:Schabus (1850) Konigliche Akademie der Wissenschaften, Vienna, Ber.: 5: 369 (artif. mat.).

Dufet (1890) Bulletin de la Société française de Minéralogie: 13: 346.

Groth, P. (1908) Chemische Krystallographie. Leipzig. 5 volumes: vol. 2: 586 (artif. mat.).

Gossner and Mussgnug (1930) Zeitschrift für Kristallographie, Mineralogie und Petrographie, Leipzig: 72: 476 (artif. mat.).

Bandy (1937) American Mineralogist: 22: 929-930.

Mémoires du Bureau de Recherches Géologiques et Minières: 8: 271-274.

Palache, Charles, Harry Berman & Clifford Frondel (1951), The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana Yale University 1837-1892, Seventh edition, Volume II: 645-646.

Brandon, J. K. & I.D. Brown (1968): "An accurate deermination of the crystal structure of triclinic potassium dichromate" Canadian Journal of Chemistry: 46: 933-941.

Brunton, G. (1983): "Refinement of the structure of K2Cr2O7": Mat. Res. Bull. 8, 271-274.

Anthony, J.W., Bideaux, R.A., Bladh, K.W., and Nichols, M.C. (2003) Handbook of Mineralogy, Volume V. Borates, Carbonates, Sulfates. Mineral Data Publishing, Tucson, AZ, 813pp.: 411.

Internet Links for Lópezite

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  • Raman and XRD data at RRUFF project
  • American Mineralogist Crystal Structure Database
  • Search for Lópezite in the Natural History Museum (London) online catalogue
  • Lopezite details from Handbook of Mineralogy (PDF)
    • Mineral Dealers:
  • Wilensky Fine Minerals
  • Fabre Minerals - search for Lópezite specimens
  • rare and unusual minerals mainly crystallized
  • Rare and Unusual minerals at Mineralogical Research Company
  • Buy fine minerals and gemstones from Pala International
  • Find Lópezite on www.crystalclassics.co.uk
  • SpiriferMinerals.com - high quality specimens
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    Localities for Lópezite

    Hide Locality List
    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.
    Chile
     
    • Antofagasta Region
      • Tocopilla Province
        • Oficina Maria Elena
    		Palache, C., Berman, H., & Frondel, C. (1951), The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana, Yale University 1837-1892, Volume II: 646; O'Donoghue (1978) "Encyclopedia of Minerals & Gemstones", p283.
    • Tarapacá Region
      • Iquique Province
    		Bandy (1937) American Mineralogist: 22: 929-930.
    Handbook of Mineralogy - Anthony, Bideaux, Bladh, Nichols; American Mineralogist: 79: 1003-1008.
    South Africa
     
    • Limpopo Province
      • Bushveld Complex
    		www.fc.up.pt/geo/ecrofi/377.PDF.
    Mineral and/or Locality
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