THOROGUMMITE
thorogummite - mineral 51.5.2.5

	Chemical Formula	Th(SiO4)1-x(OH)4x
	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. The more hydroxyl there is present, the less silica there is present. Thorogummite often contains some uranium partially replacing the thorium.
	Variable Formula	(Th,U)(SiO4)1-x(OH)4x
	Color	Reddish-brown, greenish-brown, and yellowish-brown
	Streak	Light brown
	Hardness	4½
	Crystal Forms and Aggregates	(Tetragonal) Thorogummite is always a replacement pseudomorph of the mineral Thorite, and thus occurs in the same crystals as Thorite. (Thorite crystals are occasionally short and stubby, and are usually terminated. They are rarely as elongated prisms.) However, Thorogummite rarely occurs in crystals, since forms from the radioactive decay (metamiction) of Thorite. This causes the crystals to lose their shape and become massive-shaped. Upon the rare event that Thorogummite is in crystal form, the crystals are always rounded at the edges, with a domal shape. Thorite (and, for that matter, Thorogummite) most often occurs grainy, reniform, as fibrous masses, and massive.
	Transparency	Opaque
	Specific Gravity	4.0 - 5.5 (Dependent upon the amount of hydroxyl present)
	Luster	Resinous to pitchy
	Cleavage	3,2
	Fracture	Conchoidal to splintery. Massive specimens are earthy.
	Tenacity	Brittle
	Other Names	Mackintoshite
	In Group	Silicates ; Nesosilicates
	All About	Thorogummite is often thought to be a variety of the mineral Thorite. However, it is a scientifically different mineral, and is always a replacement pseudomorph after Thorite. Thorogummite forms when Thorite starts decaying from radioactive self-destruction (a process known as metamiction). 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 a new mineral, Thorogummite, is formed. Thorite is a highly radioactive mineral, and it must be stored with all the precautions exercised with radioactive minerals.
	Uses	Thorogummite is an increasingly important ore of the radioactive element thorium.
	Striking Features	Color, luster, and strong radioactivity
	Popularity (1-4)	3
	Prevalence (1-3)	3
	Demand (1-3)	2
	Distinguishing Similar Minerals	Carnotite and Tyuyamunite- softer and lighter in weight Zircon and Hafnon - harder, different streak See also Thorite
	Commonly Occurs With	Thorite, Quartz, Biotite, Orthoclase, Monazite, Xenotime, Betafite
	Noteworthy Localities	Thorogummite is found in all localities containing Thorite where the Thorite has undergone metamiction. These localities includes Arendal, Langesundfjord, and Lomo, Norway; the Eifel Mountains, Germany; Bancroft, Hastings Co., Ontario; the Thomas Range, Juab Co., Utah; and Llano Co., Texas.
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Additional references

• The Mineral Gallery (Amethyst Galleries)
• Mineralogy Database (David Barthelmy)
• Alkali-Nuts (Marc Favre)