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Gemstones 250x250

The Mineral thorogummite

Thorogummite with Thorite in Barite

Thorogummite is always a replacement pseudomorph after Thorite, and is sometimes thought as being a variety of that mineral. However, Thorogummite is regarded by the IMA as a distinct mineral species with its own chemical formula. It forms when Thorite starts decaying from the radioactive metamiction process. When this happens, its crystal edges become rounded and smooth, and it eventually loses some silica (SiO4) molecules in its structure. The areas in the structure where the silica molecules were are replaced by hydroxyl (OH) molecules, and thus begins the transformation into Thorogummite.


Thorogummite is a highly radioactive mineral, and should be stored with all the precautions exercised with radioactive minerals.

Chemical Formula

Th(SiO4)1-x(OH)4x

Color

Reddish-brown, greenish-brown, and yellowish-brown

Crystal System

Tetragonal

Properties

Streak
Light brown
Hardness
4.5
Transparency
Opaque
Specific Gravity
4.0 - 5.5
Luster
Resinous to pitchy
Cleavage
3,2
Fracture
Conchoidal to splintery. Massive specimens are earthy.
Tenacity
Brittle

Crystal Habits

Thorogummite is always a replacement pseudomorph of Thorite, and will form in the same crystal habits as Thorite, which are stubby or prismatic and usually terminated. However, Thorogummite is rarely in crystals due to metamiction, which causes its crystal lattice to break down and lose its shape. Thorogummite is most often massive, grainy, reniform, and in fibrous masses.

Additional Information

Composition
Basic thorium silicate, with a varying amount of silica (SiO4) and hydroxyl (OH). The amount of hydroxyl present is dependent on how much silica is lacking. More hydroxyl means less silica. Thorogummite may also contain some uranium partially replacing the thorium.
In Group
Silicates; Nesosilicates
Striking Features
Color, luster, and strong radioactivity
Environment
In weathered rare earth granite pegmatites.
Rock Type
Igneous

Other Names

Mackintoshite

Uses

Thorogummite is an ore of the radioactive element thorium.

Noteworthy Localities

Thorogummite is found in localities containing Thorite where the Thorite has undergone metamiction. Localities includes Arendal, Langesundfjord, Norway; the Laach Lake Volcanic Complex, Eifel Mountains, Germany; the Bancroft District, Hastings Co., Ontario; the Thomas Range, Juab Co., Utah; the Seerie pegmatite, Jefferson Co., Colorado; and Barringer Hill, Llano Co., Texas.

Common Mineral Associations

Thorite, Quartz, Biotite, Orthoclase, Monazite, Xenotime, Betafite

Distingushing Similar Minerals

Carnotite and Tyuyamunite - Softer and lighter in weight.
Zircon and Hafnon - Harder, different streak.

thorogummite Photos



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