Lópezite
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Formula:
K2Cr2O7
System:
Triclinic
Colour:
Orange-red, red
Lustre:
Vitreous
Hardness:
2½
Name:
For Emiliano López Saa (1871-1959), Chilean mining engineer and mineral collector associated with the Chilean nitrate mining industry.
Note: Most commercially available "lópezite" is, in fact, synthetic K2Cr2O7.
Classification of Lópezite
Approved, 'Grandfathered' (first described prior to 1959)
6/F.05-10
7.FD.05
7 : SULFATES (selenates, tellurates, chromates, molybdates, wolframates)
F : Chromates
D : Dichromates
7 : SULFATES (selenates, tellurates, chromates, molybdates, wolframates)
F : Chromates
D : Dichromates
Dana 7th ed.:
35.2.1.1
35.2.1.1
35 : ANHYDROUS CHROMATES
2 : A2X2O7
35 : ANHYDROUS CHROMATES
2 : A2X2O7
27.2.2
27 : Sulphites, Chromates, Molybdates and Tungstates
2 : Chromates
27 : Sulphites, Chromates, Molybdates and Tungstates
2 : Chromates
Physical Properties of Lópezite
Vitreous
Diaphaneity (Transparency):
Transparent
Colour:
Orange-red, red
Streak:
light yellow
Hardness (Mohs):
2½
Cleavage:
Perfect
[010] perfect, [100] distinct, [001] distinct
[010] perfect, [100] distinct, [001] distinct
Density:
2.69 g/cm3 (Measured) 2.704 g/cm3 (Calculated)
Optical Data of Lópezite
Type:
Biaxial (+)
RI values:
nα = 1.714 nβ = 1.732 nγ = 1.805
2V:
Measured: 50° , Calculated: 56°
Max Birefringence:
δ = 0.091
Image 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
Y = yellow
Z = greenish yellow
Chemical Properties of Lópezite
Formula:
K2Cr2O7
Elements listed in formula:
Crystallography of Lópezite
Crystal System:
Triclinic
Class (H-M):
1 - Pinacoidal
Space Group:
P1
Cell Parameters:
a = 7.46 Å, b = 13.4 Å, c = 7.38 Å
α = 90.75°, β = 96.21°, γ = 97.96°
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 Data:
| d-spacing | Intensity |
|---|---|
| 4.87 | (45) |
| 3.658 | (85) |
| 3.472 | (80) |
| 3.298 | (100) |
| 3.063 | (30) |
| 3.027 | (30) |
| 2.877 | (30) |
Comments:
synthetic (ICDD 27-0380)
Type Occurrence of Lópezite
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
Geological Setting of Type Material:
nitrate rock
Empirical Formula:
K2[Cr26+O7]
Associated Minerals at Type Locality:
Relationship of Lópezite to other Species
| 27.2.1 | Tarapacáite | K2(CrO4) |
| 27.2.3 | Chromatite | CaCr6+O4 |
| 27.2.4 | Hashemite | Ba(CrO4) |
| 27.2.5 | Crocoite | Pb(CrO4) |
| 27.2.6 | Phoenicochroite | Pb2(CrO4)O |
| 27.2.7 | Santanaite | Pb11(CrO4)O12 |
| 27.2.8 | Iranite | Pb10Cu(CrO4)6(SiO4)2(OH)2 |
| 27.2.9 | Hemihedrite | Pb10Zn(CrO4)6(SiO4)2(OH)2 |
Other Names for Lópezite
Other Information
Other Information:
Readily soluble in water.
Health Risks:
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) Königliche Akademie der Wissenschaften, Vienna, Ber.: 5: 369 [artificial material].
Dufet (1890) Bulletin de la Société française de Minéralogie: 13: 346.
Groth, P. (1908) Chemische Krystallographie. Leipzig. 5 volumes: vol. 2: 586 [artificial material].
Gossner and Mussgnug (1930) Zeitschrift für Kristallographie, Mineralogie und Petrographie, Leipzig: 72: 476 [artificial material].
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. & Brown, I. D. (1968): An accurate determination 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.
Dufet (1890) Bulletin de la Société française de Minéralogie: 13: 346.
Groth, P. (1908) Chemische Krystallographie. Leipzig. 5 volumes: vol. 2: 586 [artificial material].
Gossner and Mussgnug (1930) Zeitschrift für Kristallographie, Mineralogie und Petrographie, Leipzig: 72: 476 [artificial material].
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. & Brown, I. D. (1968): An accurate determination 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
mindat.org URL:
https://www.mindat.org/min-2433.html
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Localities for Lópezite
This map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the 
symbol to view information about a locality.
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(TL) indicates type locality for a valid mineral species. (FRL) indicates first recorded locality for everything else. ? 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 | |
| Uwe Kolitsch collection (anthropogenic?) |
Chile | |
| 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. |
| Bandy (1937) American Mineralogist: 22: 929-930. |
| Handbook of Mineralogy - Anthony, Bideaux, Bladh, Nichols; American Mineralogist: 79: 1003-1008. | |
South Africa | |
| www.fc.up.pt/geo/ecrofi/377.PDF.; McDonald, I., Vaughan, D. J., & Tredoux, M. (1995). Platinum mineralization in quartz veins near Naboomspruit, central Transvaal. S. Afr. J. Geol, 98, 168-175. |
Oficina Maria Elena, Tocopilla Province, Antofagasta Region, Chile