The Mineral thorogummite

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.

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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