Francevillite

Discovered in 1957; IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

(Ba,Pb)(UO₂)₂(V₂O₈) · 5H₂O

Hydrated Barium Lead Uranyl Vanadate

Molecular Weight:

978.77 gm

Composition:

Barium

10.52 %

Ba

11.75 %

BaO

Uranium

48.64 %

U

55.18 %

UO₂

Vanadium

10.41 %

V

18.58 %

V₂O₅

Hydrogen

0.62 %

H

5.52 %

H₂O

Lead

5.29 %

Pb

5.70 %

PbO

Oxygen

24.52 %

O

100.00 %

96.73 %

= TOTAL OXIDE

Classification

Mineral Classification:

Oxides

Strunz 8th Ed. ID:

7/E.11-100

Nickel-Strunz 10th Ed. ID:

4.HB.15

4 : OXIDES (Hydroxides, V[5,6] vanadates, arsenites, antimonites, bismuthites, sulfites, selenites, tellurites, iodates)
H : V[5,6] Vanadates
B : Uranyl Sorovanodates

Related to:

Curienite-Francevillite Series.

Varieties:

None

Synonyms:

Barium-Francevillite

Crystal Data

Crystallography:

Orthorhombic - Dipyramidal

Crystal Habit:

Commonly as crystals, dominantly {111}, rare {100}, {010}, a few other forms, to 8 mm, in aggregates and crusts. Also massive, in veinlets and as impregnations.

Twinning:

None

Physical Properties

Cleavage:

Perfect on {001}

Fracture:

n/a

Tenacity:

Brittle

Moh's Hardness:

3.0

Density:

4.55 (g/cm³)

Luminescence:

None

Radioactivity:

Very Strong; GRapi = 3,545,303.50 (Gamma Ray American Petroleum Institute Units)

Health Warning:

Contains uranium - always wash hands after handling. Avoid inhaling dust when handling or breaking. Never lick or ingest. Avoid prolonged exposure in proximity of the body. Store away from inhabited areas.

Optical Properties

Color:

Lemon-yellow, yellow-orange, orange, greenish yellow; green, brown.

Transparency:

Semi-transparent

Luster:

Adamantine, pearly

Refractive Index:

1.750 - 2.002  Biaxial ( - )

Birefringence:

0.195 - 0.217

Dispersion:

Strong

Pleochroism:

X = colorless; Y = Z = yellow

Occurances

Geological Setting:

In the oxidized zone of a Pb-bearing U–V deposit (Mounana mine, Gabon).

Common Associations:

Curienite, Duttonite, Vanuralite, Chervetite, Mottramite, Mounanaite, Carnotite, Dewindtite, Torbernite, Uranopilite, Johannite, Kasolite (Mounana mine, Gabon)

Common Impurities:

None

Type Locality:

Mounana Mine (Mouana Mine), Franceville, Haut-Ogooué Province, Gabon

Year Discovered:

1957

View mineral photos:

Francevillite Mineral Photos and Locations

Unusual Gem Categories

Radioactive Gems

More Information

Mindat.org
Webmineral.com

Francevillite is a rare barium lead uranyl vanadate mineral that is strongly radioactive due to its uranium content. Francevillite occurs in the oxidized zone of lead-bearing uranium–vanadium deposits. It was first described in 1957 from an occurrence at the Mounana (uranium) Mine, near Franceville, Haut-Ogooué, Gabon and was named for the nearby city of Franceville. Francevillite occurs as crystals to about 8 mm, and as aggregates, massive, in veinlets and as impregnations. Its colors range from lemon-yellow to yellow-orange and orange, greenish yellow, green and brown. Francevillite is semi-transparent with adamantine to pearly luster, strong dispersion and Mohs hardness of 3.

Francevillite distribution: exceptional crystals from the Mounana uranium Mine, Franceville, Gabon. At Kambove and in the Musonoi mine, near Kolwezi, Katanga Province, Congo (Shaba Province, Zaire). On the southwest edge of the Chimeja Range, about four km north of Lubimbi Spring, Zimbabwe. From Bertholène and Lussagues, Aveyron, and Saint-Pierre, Cantal, France. In Germany, on the Donnersberg, near Imsbach, Rhineland-Palatinate; in the Black Forest, at Nussbach, near Triberg, and from the Clara mine, near Oberwolfach. In the South Terras mine, St. Stephen-in-Brannel, Cornwall, England. At the Tyuya-Muyun Cave, Fergana Valley, Alai Range, Kyrgyzstan. From the Otish Mountains, Quebec, Canada. In the USA, at Jim Thorpe, Carbon County, Pennsylvania.

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