Fornacite Mineral Data

Fornacite Mineral Data +

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General Fornacite Information

Chemical Formula:

Pb2Cu(CrO4)(AsO4)(OH)

Composition:

Molecular Weight = 749.87 gm

Chromium 6.93 % Cr 13.33 % CrO₃

Copper 8.47 % Cu 9.54 % Cu₂O

Arsenic 9.99 % As 15.33 % As₂O₅

Hydrogen 0.13 % H 1.20 % H₂O

Lead 55.26 % Pb 59.53 % PbO

Oxygen 19.20 % O

______ ______

100.00 % 98.93 % = TOTAL OXIDE

Empirical Formula:

Pb₂Cu(AsO₄)(CrO₄)(OH)

Environment:

Oxidized zones of some hydrothermal base-metal deposits.

IMA Status:

Valid Species (Pre-IMA) 1915

Locality:

Djoue and Reneville, Congo Republic. Link to MinDat.org Location Data.

Name Origin:

Named for Lucien Lewis Forneau (1867-1930), Colonial Governor of the French Congo.

Synonym:

ICSD 26828

PDF 15-200

Fornacite Image

Images:

Fornacite

Comments: Dark, prismatic crystals of fornacite on matrix.
Location: El Khun mine, Anarak, Iran. Scale: Not Given.
© Lou Perloff / Photo Atlas of Minerals

Images:

Fornacite

Comments: Emerald green platy crystals to 0.75mm on a pink to white, siliceous matrix.
Location: Lone Star mine, Copperopolis, Yavapai County, Arizona. Scale: Picture size 1.4 cm.
© Tom Loomis / Dakota Matrix

Fornacite Crystallography

Axial Ratios:

a:b:c =1.3384:1:2.9543

Cell Dimensions:

a = 7.91, b = 5.91, c = 17.46, Z = 4; beta = 108° V = 776.27 Den(Calc)= 6.42

Crystal System:

Monoclinic - PrismaticH-M Symbol (2/m) Space Group: P 2₁/c

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

By Intensity(I/I_o): 2.88(1), 2.98(1), 3.31(1),

Crystal Structure:

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Cocco G , Fanfani L , Zanazzi P F , Zeitschrift fur Kristallographie , 124 (1967) p.385-397, The crystal structure of fornacite, Locality: Reneville, Congo

Physical Properties of Fornacite

Cleavage:

None

Color:

Green, Yellow, Olive green, Greenish yellow.

Density:

6.27

Diaphaniety:

Transparent to Translucent

Fracture:

Conchoidal - Fractures developed in brittle materials characterized by smoothly curving surfaces, (e.g. quartz).

Habit:

Aggregates - Made of numerous individual crystals or clusters.

Hardness:

2-3 - Gypsum-Calcite

Luster:

Vitreous (Glassy)

Streak:

greenish yellow

Optical Properties of Fornacite

Gladstone-Dale:

CI meas= -0.084 (Poor) - where the CI = (1-KPDmeas/KC)
CI calc= -0.059 (Good) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.1854,KPDmeas= 0.1898,KC= 0.1751

Optical Data:

Biaxial (+), a=2.14, g=2.24, bire=0.1000, 2V(Meas)=large.

Calculated Properties of Fornacite

Electron Density:

r_electron=5.53 gm/cc
note: r_Fornacite=6.42 gm/cc.

Fermion Index

Fermion Index = 0.12881
Boson Index = 0.87119

Photoelectric:

PE_Fornacite= 998.15 barns/electron
U=PE_Fornacite x r_electron=5,520.53 barns/cc.

Radioactivity:

GRapi = 0 (Gamma Ray American Petroleum Institute Units)

Fornacite is Not Radioactive

Fornacite Classification

Dana Class:

43.4.3.2 (43)Compound Phosphates, etc.

(43.4)(Anhydrous Compound Anions With Hydroxyl or Halogen)

(43.4.3)Brackebushite Group

43.4.3.1 Vauquelinite Pb2Cu(CrO4)(PO4)(OH) P 2₁/n 2/m

43.4.3.2 Fornacite Pb2Cu(CrO4)(AsO4)(OH) P 2₁/c 2/m

43.4.3.3 Molybdofornacite Pb2Cu[(As,P)O4][(Mo,Cr)O4](OH) P 2₁/c 2/m

Strunz Class:

VI/F.02-20 VI - Sulfates,Chromates,Molybdates and Tungstates

VI/F - Chromates [CrO4]2-

VI/F.02 - Wattersite - Satanaite series

VI/F.02-03 Wattersite Hg4HgCrO6 C 2/c 2/m

VI/F.02-05 Edoylerite Hg3CrO4S2 P 2₁/a 2/m

VI/F.02-07 Deanesmithite Hg2Hg3CrO5S2 P1 1

VI/F.02-10 Vauquelinite Pb2Cu(CrO4)(PO4)(OH) P 2₁/n 2/m

VI/F.02-20 Fornacite Pb2Cu(CrO4)(AsO4)(OH) P 2₁/c 2/m

VI/F.02-30 Molybdofornacite Pb2Cu[(As,P)O4][(Mo,Cr)O4](OH) P 2₁/c 2/m

VI/F.02-40 Phoenicochroite Pb2(CrO4)O C 2/m 2/m

VI/F.02-50 Santanaite Pb9Pb2CrO16 P 6₃22 6 2 2

Other Fornacite Information

References:

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

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Fornacite

Pb2Cu(CrO4)(AsO4)(OH)
Dana No: 43.4.3.2 Strunz No: VI/F.02-20
Locality:

Notes: