Tarapacaite Mineral Data

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General Tarapacaite Information

Chemical Formula:

K2CrO4

Composition:

Molecular Weight = 194.19 gm

Potassium 40.27 % K 48.51 % K₂O

Chromium 26.78 % Cr 51.49 % CrO₃

Oxygen 32.96 % O

______ ______

100.00 % 100.00 % = TOTAL OXIDE

Empirical Formula:

K₂(CrO₄)

Environment:

Minor accessory mineral in nitrate deposits.

IMA Status:

Valid Species (Pre-IMA) 1878

Locality:

In Chile, in nitrate caliche deposits throughout the Atacama Desert. Link to MinDat.org Location Data.

Name Origin:

Named for its first noted occurrence in the Tocopilla Pampa, 170 km north of Antofagasta, Tarapaca, Chile.

Name Pronunciation:

Tarapacaite + Pronunciation

Synonym:

ICSD 2402

PDF 15-365

Tarapacaite Image

Images:

Tarapacaite

Comments: Pale brown translucent tarapacaite, deliquescent granular.
Location: Tarapaca, Chile. Scale: See Photo.
© Jeff Weissman / Photographic Guide to Mineral Species

Tarapacaite Crystallography

Axial Ratios:

a:b:c =0.7374:1:0.5696

Cell Dimensions:

a = 7.663, b = 10.391, c = 5.919, Z = 4; V = 471.31 Den(Calc)= 2.74

Crystal System:

Orthorhombic - DipyramidalH-M Symbol (2/m 2/m 2/m) Space Group: Pnam

$Help on X Ray Diffraction:$ X Ray Diffraction:

By Intensity(I/I_o): 3.078(1), 2.988(0.75), 2.96(0.4),

Crystal Structure:

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McGinnety J A , Acta Crystallographica, Section B , 28 (1972) p.2845-2852, Redetermination of the structures of potassium sulphate and potassium chromate:, the effect of electrostatic crystal forces upon observed bond length

Physical Properties of Tarapacaite

Cleavage:

{001} Distinct, {010} Distinct

Color:

Yellow, Light yellow.

Density:

2.74

Diaphaneity:

Transparent

Luster:

Vitreous (Glassy)

Streak:

light yellow

Optical Properties of Tarapacaite

Gladstone-Dale:

CI meas= 0.027 (Excellent) - where the CI = (1-KPDmeas/KC)
CI calc= 0.027 (Excellent) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.2603,KPDmeas= 0.2603,KC= 0.2676
Ncalc = 1.73

Optical Data:

Biaxial (-), a=1.687, b=1.722, g=1.731, bire=0.0440, 2V(Calc)=52, 2V(Meas)=52.

Calculated Properties of Tarapacaite

Electron Density:

Bulk Density (Electron Density)=2.65 gm/cc
note: Specific Gravity of Tarapacaite =2.74 gm/cc.

Fermion Index:

Fermion Index = 0.02
Boson Index = 0.98

Photoelectric:

PE_Tarapacaite= 10.15 barns/electron
U=PE_Tarapacaite x r_electron= 26.92 barns/cc.

Radioactivity:

GRapi = 562.48 (Gamma Ray American Petroleum Institute Units)
Concentration of Tarapacaite per GRapi unit =1,777.84 (PPM)

**Estimated Radioactivity from Tarapacaite** - mild
Specimen Size Weight/Volume (Sphere) *	Calculated Activity Bequerols (Bq)	Calculated Activity Curies (Ci)	Estimated Activity GR(api)	Estimated Exposure (mRem**)/hr If Held in Hand For One Hour
1000 gm / 8.87 cm	12,201	3.30E-07	562.48	0.18
100 gm / 4.12 cm	1,220	3.30E-08	56.25	0.02
10 gm / 1.91 cm	122	3.30E-09	5.62	0.00
1 gm / 8.87 mm	12	3.30E-10	0.56	0.00
0.1 gm / 4.12 mm	1	3.30E-11	0.06	0.00
0.01 gm / 1.91 mm	0	3.30E-12	0.01	0.00
0.001 gm / 0.89 mm	0	3.30E-13	0.00	0.00

Weight of pure Tarapacaite in grams (gm) and Calculated Diameter of a Sphere with a Density of 2.74 gm/cc.*
Goverment Estimate of Average Annual Exposure ( 360 mRem) **
Note: 10 microsieverts/hr = 1 mRem/hr **
Max Permissable Adult Dose 50,000 mRem/yr (hands), 15,000 mRem/yr (eyes)
Lethal Dose LD(50) Exposure 400,000 to 500,000 mRem

Tarapacaite Classification

Dana Class:

35.01.01.01 (35)Anhydrous Chromates

(35.01)where (A+)2 XO4

(35.01.01)Dana Group

35.01.01.01 Tarapacaite K2CrO4 Pnam 2/m 2/m 2/m

Strunz Class:

07.FA.05 07 - SULFATES (SELENATES, TELLURATES)

07.F - Chromates

07.FA -Without additional anions

07.FA.05 Tarapacaite K2CrO4 Pnam 2/m 2/m 2/m

Other Tarapacaite Information

References:

NAME( AntBidBlaNic4) PHYS. PROP.(Enc. of Minerals,2nd ed.,1990) OPTIC PROP.(Enc. of Minerals,2nd ed.,1990)

See Also:

Links to other databases for Tarapacaite :
1 - Am. Min. Crystal Structure Database
2 - Athena
3 - EUROmin Project
4 - Ecole des Mines de Paris
5 - Google Images
6 - Google Scholar
7 - Handbook of Mineralogy (MinSocAm)
8 - Handbook of Mineralogy (UofA)
9 - MinDAT
10 - MinMax(Deutsch)
11 - MinMax(English)
12 - Mineralienatlas (Deutsch)
13 - QUT Mineral Atlas
14 - Ruff.Info

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Print or Cut-and-Paste your Tarapacaite Specimen Label here :

Tarapacaite

K2CrO4
Dana No: 35.01.01.01 Strunz No: 07.FA.05
Locality:

Notes: