Thorite
The mineral thorite is a rarely occurring silicate from the island Zirkongruppe and has the chemical composition (Th, U) [ SiO4 ]. By substitution, it can contain considerable amounts of other elements, particularly zirconium and uranium instead of thorium.
It crystallizes in the tetragonal crystal system and usually develops square, prismatic or pseudo- octahedral crystals to about 8 cm in size, but also massive aggregates of yellow-orange, brownish yellow, brown to black, rarely green color and light orange to dark brown stroke color.
Special Features
The mineral is characterized by its content of thorium ( max. 71.6 %) classified and uranium ( depending on the degree of substitution of thorium) as highly radioactive and has a specific activity of about 32 kBq / g (compared to natural potassium 31.2 Bq / g). Due to the high radioactivity, it is also often metamict, ie its crystal lattice is destroyed, color also becomes darker by the increasing destruction of the crystal lattice, from brown to finally black.
Etymology and history
Was first discovered in 1828 by the parish priest Thorit Esmark on the Norwegian island Løvøya ( Løvø ) in Langesundfjord in the Norwegian county of Telemark and scientifically described in 1829 by Jöns Jakob Berzelius, who named the mineral after contained in the formula chemical element thorium.
Classification
In the now outdated but still in use 8th edition of the mineral classification by Strunz the Thorit belonged to the department of " island silicates ( nesosilicates ) ", where he formed a distinct group with coffinite, Hafnon, Reidit, thorogummite and zircon.
The valid since 2001 and used by the IMA 9th edition of the Strunz'schen Mineral classification assigns the Thorit also in the department of " island silicates ". This division, however, is further subdivided by the presence of other anions and the coordination of the cations, so that the mineral according to its composition in the subdivision of " island silicates without other anions; can be found with cations in oktahedraler and usually greater coordination ", where it forms together with the unnamed group 9.AD.30.
The classification of minerals according to Dana assigns the Thorit also included in the category of " silicates and Germanates " and then in the Department of the " island silicates ". There he is, also together with coffinite, Hafnon, thorogummite and zirconium, in the " Zirkongruppe " with the system no. 51.05.02 found within the subdivision " island silicates with SiO4 groups and only with cations in > coordination ".
Modifications and varieties
The compound ( Th, U ) [ SiO4 ] is polymorphic, ie they occur in nature in addition to the tetragonal thorite as monoclinic huttonite on.
Orangit is a crystallized, orange or yellow variety of thorite; Uranothorit with lots of U, MacIntoshit with U and Ce, Auerlith with P instead of Si.
Education and Locations
Thorite is a typical mineral in granitic pegmatites, which are enriched in incompatible elements. Furthermore, Thorit found in very small quantities in many igneous and metamorphic rocks. Accompanying minerals include zircon, monazite, Gadolinit, fergusonite, uraninite, Yttrialit and pyrochlore.
Worldwide, Thorit so far (as of 2010) are detected at around 660 localities, as in Egypt, Armenia, Australia, Bolivia, Brazil, China, Germany, Finland, France, Greenland, Guyana, India, Indonesia, Italy, Japan, Canada, Kazakhstan, Kyrgyzstan, North and South Korea, Madagascar, Malawi, Morocco, Mexico, Mongolia, Myanmar, New Zealand, Nigeria, Norway, Austria, Pakistan, Paraguay, Poland, Portugal, Russia, Zambia, Saudi Arabia, Sweden, Slovakia, Spain, Swaziland, South Africa, Tajikistan, Czech Republic, Ukraine, Hungary and the United States of America (USA).
Crystal structure
Thorit crystallized tetragonal in the space group I41/amd with the lattice parameters a = 7.13 Å and c = 6.32 Å and four formula units per unit cell.