Lópezite
A valid IMA mineral species - grandfathered
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About Lópezite
Formula:
K2Cr6+2O7
Colour:
Orange-red, red
Lustre:
Vitreous, Resinous
Hardness:
2½
Specific Gravity:
2.69
Crystal System:
Triclinic
Name:
Named by Mark C. Bandy in 1937 for Emiliano López Saa (1871-1959), Chilean mining engineer and mineral collector associated with the Chilean nitrate mining industry. Previously, the substance was known only as a synthetic compound.
Type Locality:
Note: Most commercially available "lópezite" is, in fact, synthetic K2Cr2O7.
Several synthetic polymorphs are known.
Several synthetic polymorphs are known.
Name Encoding
ASCII-7:
Lopezite
Unique Identifiers
Mindat ID:
2433
Long-form identifier:
mindat:1:1:2433:0
IMA Classification of Lópezite
Approved, 'Grandfathered' (first described prior to 1959)
First published:
1937
Type description reference:
Classification of Lópezite
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
Mineral Symbols
As of 2021 there are now IMA–CNMNC approved mineral symbols (abbreviations) for each mineral species, useful for tables and diagrams.
| Symbol | Source | Reference for Standard |
|---|---|---|
| Lpz | IMA–CNMNC | Warr, L.N. (2021). IMA–CNMNC approved mineral symbols. Mineralogical Magazine, 85(3), 291-320. doi:10.1180/mgm.2021.43 |
Physical Properties of Lópezite
Vitreous, Resinous
Transparency:
Transparent
Colour:
Orange-red, red
Streak:
Light yellow
Hardness:
2½ on Mohs scale
Tenacity:
Brittle
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
Based on recorded range of RI values above.
Based on recorded range of RI values above.
Interference Colours:
The colours simulate birefringence patterns seen in thin section under crossed polars. They do not take into account mineral colouration or opacity.
Michel-Levy Bar The default colours simulate the birefringence range for a 30 µm thin-section thickness. Adjust the slider to simulate a different thickness.
Grain Simulation You can rotate the grain simulation to show how this range might look as you rotated a sample under crossed polars. Each grain retains its interference colour (retardation) while its brightness falls to black at extinction and reaches a maximum between extinction positions.
The colours simulate birefringence patterns seen in thin section under crossed polars. They do not take into account mineral colouration or opacity.
Michel-Levy Bar The default colours simulate the birefringence range for a 30 µm thin-section thickness. Adjust the slider to simulate a different thickness.
Grain Simulation You can rotate the grain simulation to show how this range might look as you rotated a sample under crossed polars. Each grain retains its interference colour (retardation) while its brightness falls to black at extinction and reaches a maximum between extinction positions.
Surface Relief:
Moderate
Dispersion:
r > v, medium
Pleochroism:
Visible
Comments:
X = reddish yellow
Y = yellow
Z = greenish yellow
Y = yellow
Z = greenish yellow
Chemistry of Lópezite
Mindat Formula:
K2Cr6+2O7
Element Weights:
Elements listed:
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 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
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 7.31 Å | (2) |
| 6.82 Å | (10) |
| 6.60 Å | (16) |
| 6.18 Å | (2) |
| 6.04 Å | (8) |
| 5.29 Å | (4) |
| 5.13 Å | (6) |
| 5.09 Å | (18) |
| 4.95 Å | (4) |
| 4.87 Å | (45) |
| 4.52 Å | (16) |
| 4.45 Å | (40) |
| 4.17 Å | (2) |
| 3.744 Å | (16) |
| 3.09 Å | (18) |
| 3.658 Å | (85) |
| 3.472 Å | (90) |
| 3.421 Å | (10) |
| 3.408 Å | (8) |
| 3.402 Å | (6) |
| 3.349 Å | (8) |
| 3.298 Å | (100) |
| 3.281 Å | (20) |
| 3.420 Å | (12) |
| 3.219 Å | (6) |
| 3.182 Å | (4) |
| 3.137 Å | (1) |
| 3.063 Å | (30) |
| 3.027 Å | (30) |
| 3.005 Å | (25) |
| 2.945 Å | (4) |
| 2.877 Å | (30) |
| 2.857 Å | (30) |
| 2.758 Å | (6) |
| 2.712 Å | (2) |
| 2.692 Å | (2) |
| 2.641 Å | (10) |
| 2.634 Å | (4) |
Comments:
synthetic (ICDD 27-0380)
Geological Environment
Paragenetic Mode(s):
| Paragenetic Mode | Earliest Age (Ga) |
|---|---|
| Near-surface Processes | |
| 25 : Evaporites (prebiotic) | |
| Stage 10b: Anthropogenic minerals | <10 Ka |
| 56 : Slag and smelter minerals (see also #51 and #55) |
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
Associated Minerals at Type Locality:
Other Language Names for Lópezite
Common Associates
Radioactivity
Radioactivity:
| Element | % Content | Activity (Bq/kg) | Radiation Type |
|---|---|---|---|
| Uranium (U) | 0.0000% | 0 | α, β, γ |
| Thorium (Th) | 0.0000% | 0 | α, β, γ |
| Potassium (K) | 26.5808% | 8,240 | β, γ |
For comparison:
- Banana: ~15 Bq per fruit
- Granite: 1,000–3,000 Bq/kg
- EU exemption limit: 10,000 Bq/kg
Note: Risk is shown relative to daily recommended maximum exposure to non-background radiation of 1000 µSv/year. Note that natural background radiation averages around 2400 µSv/year so in reality these risks are probably extremely overstated! With infrequent handling and safe storage natural radioactive minerals do not usually pose much risk.
Interactive Simulator:
Note: The mass selector refers to the mass of radioactive mineral present, not the full specimen, also be aware that the matrix may also be radioactive, possibly more radioactive than this mineral!
Activity: –
| Distance | Dose rate | Risk |
|---|---|---|
| 1 cm | ||
| 10 cm | ||
| 1 m |
The external dose rate (D) from a radioactive mineral is estimated by summing the gamma radiation contributions from its Uranium, Thorium, and Potassium content, disregarding daughter-product which may have a significant effect in some cases (eg 'pitchblende'). This involves multiplying the activity (A, in Bq) of each element by its specific gamma ray constant (Γ), which accounts for its unique gamma emissions. The total unshielded dose at 1 cm is then scaled by the square of the distance (r, in cm) and multiplied by a shielding factor (μshield). This calculation provides a 'worst-case' or 'maximum risk' estimate because it assumes the sample is a point source and entirely neglects any self-shielding where radiation is absorbed within the mineral itself, meaning actual doses will typically be lower. The resulting dose rate (D) is expressed in microsieverts per hour (μSv/h).
D = ((AU × ΓU) + (ATh × ΓTh) + (AK × ΓK)) / r2 × μshield
Fluorescence of Lópezite
Not fluorescent in UV
Other Information
Notes:
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.
Internet Links for Lópezite
mindat.org URL:
https://www.mindat.org/min-2433.html
Please feel free to link to this page.
Please feel free to link to this page.
Search Engines:
External Links:
Mineral Dealers:
References for Lópezite
Reference List:
Goßner, B.; Mußgnug, F. (1930) Über kristallographische Beziehungen zwischen Kaliumdichromat und Ammoniumdichromat. Zeitschrift für Kristallographie, Mineralogie und Petrographie, 72 (1-6). 476-481 doi:10.1524/zkri.1930.72.1.476[artificial material]
Brandon, J. K., Brown, I. D. (1968) An accurate determination of the crystal structure of triclinic potassium dichromate, K2Cr2O7. Canadian Journal of Chemistry, 46 (6). 933-941 doi:10.1139/v68-155
Brunton, George (1973) Refinement of the structure of K2Cr2O7. Materials Research Bulletin, 8 (3). 271-274 doi:10.1016/0025-5408(73)90004-4
Krivovichev, Sergey V., Kir'yanova, Elena V., Filatov, Stanislav K., Burns, Peter C. (2000) β-K2Cr2O7. Acta Crystallographica Section C Crystal Structure Communications, 56 (6) 629-630 doi:10.1107/s0108768100003918
Weakley, T. J. R., Ylvisaker, E. R., Yager, R. J., Stephens, J. E., Wiegel, R. D., Mengis, M., Bauer, M. R., Wu, P., Photinos, P., Abrahams, S. C. (2004) Phase transitions in K2Cr2O7 and structural redeterminations of phase II. Acta Crystallographica Section B Structural Science, 60 (6). 705-715 doi:10.1107/s010876810402333x
Localities for Lópezite
Showing 5 localities.
symbol to view information about a locality.
The Locality List
- This locality has map coordinates listed.
- This locality has estimated coordinates.
ⓘ - Click for references and further information on this occurrence.
? - Indicates mineral may be doubtful at this locality.
- Good crystals or important locality for species.
- World class for species or very significant.
(TL) - Type Locality for a valid mineral species.
(FRL) - First Recorded Locality for everything else (eg varieties).
All localities listed without proper references should be considered as questionable.
Canada | |
| Uwe Kolitsch collection (anthropogenic?) |
Chile | |
| Palache et al. (1951) +1 other reference |
| Konnert et al. (1994) +1 other reference |
| Bandy (1937) |
South Africa | |
| www.fc.up.pt/geo/ecrofi/377.PDF. +1 other reference |
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Oficina María Elena, María Elena, Tocopilla Province, Antofagasta, Chile