Coffinite  
Current inventory:  0 gems
 

  
Coffinite was named in honor of Reuben Clare Coffin (1886-1972), Tulsa, Oklahoma, USA, pioneer geologist in the study of uranium deposits of the Colorado Plateau.

Discovered in 1954;   IMA status:  Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

U(SiO₄)_1-x(OH)_4x

Uranium Silicate Hydroxide

Molecular Weight:

327.71 gm

Composition:

Uranium

72.63 %

U

82.40 %

UO₂

Silicon

7.71 %

Si

16.50 %

SiO₂

Hydrogen

0.12 %

H

1.10 %

H₂O

Oxygen

19.53 %

O

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

Silicates (Germanates)

Strunz 8th Ed. ID:

8/A.09-40

Nickel-Strunz 10th Ed. ID:

9.AD.30

9 : SILICATES (Germanates)
A : Nesosilicates
D : Nesosilicates without additional anions; cations in [6] and/or greater coordination

Related to:

Zircon Group.

Varieties:

None

Synonyms:

None

Crystal Data

Crystallography:

Tetragonal - Ditetragonal Dipyramidal

Crystal Habit:

As crystals, rarely > 20 µm, and in colloform to botryoidal incrustations, radially fibrous. Commonly pulverulent, in aggregates of extremely fine crystallites, or massive.

Twinning:

None

Physical Properties

Cleavage:

None

Fracture:

Irregular to Sub-Conchoidal

Tenacity:

Brittle or Friable

Moh's Hardness:

5.0 - 6.0

Density:

5.10 (g/cm³)

Luminescence:

None

Radioactivity:

Very Strong; GRapi = 5,176,587.32 (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:

Black from included organic matter; pale Brown to dark Brown in thin section.

Transparency:

Opaque, Transparent on very thin edges.

Luster:

Dull to Adamantine

Refractive Index:

1.730 - 1.750  Isotropic due to fine grain size; Uniaxial ( +/- )

Birefringence:

0.000  (Isotropic)

Dispersion:

n/a

Pleochroism:

Moderate; pale yellow-brown parllel to length, medium brown perpendicular to length.

Occurances

Geological Setting:

In Colorado Plateau-type black unoxidized U-V deposits, replacing organic material in sandstone; in other sedimentary and hydrothermal vein uranium deposits.

Common Associations:

Uraninite, Thorite, Pyrite, Marcasite, Roscoelite, clay minerals, amorphous organic matter.

Common Impurities:

Al, Fe, As, V, Pb

Type Locality:

La Sal No. 2 Mine, Beaver Mesa, Mesa Co., Colorado, USA

Year Discovered:

1954

View mineral photos:

Coffinite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Coffinite is a highly radioactive silicate mineral that is a member of the Zircon Group of minerals that includes Coffinite, Hafnon, Thorite, Thorogummite and Zircon. It is extremely rare and mainly for collectors of rare and unusual gems, black gems or radioactive gems. Coffinite contains over 72% unranium and surpases Autunite, Thorianite and Thorite in radioactivity. It should be stored away from other minerals and gems that might be damaged by radioactivity. Human contact and exposure to Coffinite mineral specimens or gems should be limited!

There are numerous minor occurrences of Coffinite; those mentioned are for well-crystallized or studied material. In the USA, in the La Sal No. 2 mine, Beaver Mesa, Gateway district, Mesa County, and in the Peanut mine, Montrose County, Colorado; Mount Pisgah San Bernardino County, California; around the Jackpile and Crownpoint mines, Valencia County, New Mexico; in the Mi Vida, Homestake, and other mines, San Juan County, Utah. From Wölsendorf, Bavaria; at Niederramstadt, near Schneeberg, Johanngeorgenstadt, and Niederpfannenstiel, Saxony, Germany. At Hüttenberg, Carinthia, Austria. From Jáchymov (Joachimsthal) and Pribram, Czech Republic. In the Geevor mine, St. Just, the South Terras mine, St. Stephen-in-Brannel, and the Roskrow United mine, Ponsansooth, Cornwall, England.
 

  
Coffinite gems for sale:

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