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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 (SiO 4) 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. |
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Chemical Formula |
Th(SiO4)1-x(OH)4x |
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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. |
| Variable Formula |
(Th,U)(SiO4)1-x(OH)4x |
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Color |
Reddish-brown, greenish-brown, and yellowish-brown |
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Streak |
Light brown |
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Hardness |
4.5 |
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Crystal System |
Tetragonal |
Crystal Forms
and Aggregates |
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. |
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Transparency |
Opaque |
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Specific Gravity |
4.0 - 5.5 |
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Luster |
Resinous to pitchy |
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Cleavage |
3,2 |
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Fracture |
Conchoidal to splintery. Massive specimens are earthy. |
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Tenacity |
Brittle |
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In Group |
Silicates; Nesosilicates |
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Striking Features |
Color, luster, and strong radioactivity |
| Environment |
In weathered rare earth granite pegmatites. |
| Rock Type |
Igneous |
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Popularity (1-4)
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3 |
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Prevalence (1-3)
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3 |
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Demand (1-3) |
2 |
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Thorogummite is an ore of the radioactive element thorium.
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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.
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Carnotite and Tyuyamunite - Softer and lighter in weight.
Zircon and Hafnon - Harder, different streak.
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