Tarapacáite
A valid IMA mineral species - grandfathered
This page is currently not sponsored. Click here to sponsor this page.
About Tarapacáite
Coat of arms, Tarapacá, Chile
Formula:
K2(CrO4)
Colour:
Bright yellow, yellow-orange
Specific Gravity:
2.74
Crystal System:
Orthorhombic
Name:
Named after Tarapacá, Chile, a region that includes the discovery locality, Tocopilla Pampa.
Isostructural with:
Name Encoding
ASCII-7:
Tarapacaite
Unique Identifiers
Mindat ID:
3891
Long-form identifier:
mindat:1:1:3891:7
IMA Classification of Tarapacáite
Approved, 'Grandfathered' (first described prior to 1959)
IMA Formula:
K2Cr6+O4
First published:
1878
Classification of Tarapacáite
7.FA.05
7 : SULFATES (selenates, tellurates, chromates, molybdates, wolframates)
F : Chromates
A : Without additional anions
7 : SULFATES (selenates, tellurates, chromates, molybdates, wolframates)
F : Chromates
A : Without additional anions
Dana 7th ed.:
35.1.1.1
35.1.1.1
35 : ANHYDROUS CHROMATES
1 : A2XO4
35 : ANHYDROUS CHROMATES
1 : A2XO4
27.2.1
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 |
|---|---|---|
| Tpc | 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 Tarapacáite
Transparency:
Transparent
Colour:
Bright yellow, yellow-orange
Cleavage:
Distinct/Good
On {001} and {010}, distinct.
On {001} and {010}, distinct.
Density:
2.74 g/cm3 (Measured) 2.735 g/cm3 (Calculated)
Comment:
Measured value on artificial material.
Optical Data of Tarapacáite
Type:
Biaxial (-)
RI values:
nα = 1.687 nβ = 1.722 nγ = 1.731
2V:
Measured: 52° , Calculated: 52°
Max. Birefringence:
δ = 0.044
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:
Very High (positive)
Relative to Canada balsam mounting medium (n ≈ 1.537).
Relative to Canada balsam mounting medium (n ≈ 1.537).
This shows the grain boundary and Becke line effect under plane-polarised
light, based on the contrast between this mineral's average refractive
index and the mounting medium. It does not take into account mineral
colouration.
In focus
Interference Figure:
This shows the idealized biaxial acute bisectrix (Bxa) interference figure
- the conoscopic view for a grain cut perpendicular to the acute bisectrix, using
this mineral's 2V. The two small white dots mark the melatopes - the points
where the two optic axes emerge - and are shown only when they fall within the
field of view. The coloured bands are isochromatics, and the dark bands are
isogyres.
Rotate the stage: at 0°/90° the isogyres form a cross through the melatopes; at 45° they pull apart into curved hyperbolas. That splitting on rotation - absent in a uniaxial figure - is the standard diagnostic test for telling biaxial minerals from uniaxial ones. If 2V is large, the melatopes may fall outside the field of view, as they often do at the microscope too.
Rotate the stage: at 0°/90° the isogyres form a cross through the melatopes; at 45° they pull apart into curved hyperbolas. That splitting on rotation - absent in a uniaxial figure - is the standard diagnostic test for telling biaxial minerals from uniaxial ones. If 2V is large, the melatopes may fall outside the field of view, as they often do at the microscope too.
Dispersion:
r > v weak
Optical Extinction:
X = c; Y = a; Z = b.
Chemistry of Tarapacáite
Mindat Formula:
K2(CrO4)
Element Weights:
Elements listed:
Crystallography of Tarapacáite
Crystal System:
Orthorhombic
Class (H-M):
mmm(2/m2/m2/m) - Dipyramidal
Cell Parameters:
a = 7.662(1) Å, b = 10.391(1) Å, c = 5.919(1) Å
Ratio:
a:b:c = 0.737 : 1 : 0.57
Unit Cell V:
471.25 ų (Calculated from Unit Cell)
Z:
4
Morphology:
Crystals thick tabular {001}.
Twinning:
Twinning on {110} producing pseudo-hexagonal twins analogous to aragonite.
Comment:
Space group Pnam (synthetic).
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 3.078 Å | (100) |
| 2.988 Å | (75) |
| 2.960 Å | (40) |
| 2.479 Å | (25) |
| 2.286 Å | (25) |
| 2.599 Å | (22) |
| 2.570 Å | (21) |
Geological Environment
Paragenetic Mode(s):
| Paragenetic Mode | Earliest Age (Ga) |
|---|---|
| Near-surface Processes | |
| 25 : Evaporites (prebiotic) | |
| High-? alteration and/or metamorphism | |
| 33 : Minerals deposited by hydrothermal metal-rich fluids (see also [#12]) |
Type Occurrence of Tarapacáite
Place of Conservation of Type Material:
n.d.
Geological Setting of Type Material:
Nitate deposits.
Associated Minerals at Type Locality:
Synonyms of Tarapacáite
Other Language Names for Tarapacáite
Related Minerals - Strunz-mindat Grouping
| 7.FA.10 | Chromatite | CaCr6+O4 |
| 7.FA.15 | Hashemite | BaCr6+O4 |
| 7.FA.20 | Crocoite | PbCr6+O4 |
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) | 40.2680% | 12,483 | 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
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 Tarapacáite
mindat.org URL:
https://www.mindat.org/min-3891.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 Tarapacáite
Reference List:
Raimondi, Antonio (1878) Minerales del Perú - ó catálogo razonado de una coleccion que representa los principales tipos minerales de la republica con muestras de huano y restos de aves que lo han producido. J. Enrique, Lima. pp.250-253
Localities for Tarapacáite
Showing 6 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.
Chile | |
| |
| Palache et al. (1951) +2 other references |
| Palache et al. (1951) +1 other reference | |
| Anthony et al. (2003) | |
| Konnert et al. (1994) +1 other reference |
Israel | |
| Sharygin et al. (2019) |
Quick NavTopAbout TarapacáiteName EncodingUnique IdentifiersIMA Classification Classification Mineral SymbolsPhysical Properties Optical Data Chemistry Crystallography X-Ray Powder DiffractionGeological EnvironmentType Occurrence SynonymsOther LanguagesStrunz-MindatRadioactivityOther InformationInternet Links References Localities Locality List
Tarapacá, Chile