Xenotime
- Ytterspat or Ytterspath
Xenotime, outdated also known as Ytterspat or Ytterspath, is the common name for a rarely occurring mixed crystal series of the minerals xenotime - (Y) and xenotime - (Yb ) from the mineral class of " phosphates, arsenates and vanadates ." Both end members of the mixed batch, and thus also their mixed crystals crystallize in the tetragonal crystal system. Their chemical composition is represented by Y [ PO4 ] and Yb [ PO4 ], the general formula of the mixed batch is according to (Y, Yb) [ PO4 ].
Xenotimes form prismatic or tabular crystals, but also granular aggregates in the colors gray, brown, yellow or green.
Special Features
As with other minerals containing rare earth metals, depending on the deposit part of the yttrium can be substituted by uranium or thorium. This results in a slight radioactivity. The specific activity is the xenotime - (Yb ) with about 1,446 kBq / g specified (for comparison: natural potassium 31.2 Bq / g).
Etymology and history
The word derives from the Greek xenotime κευός KENOS for " vain ", "apparently" and τιμή Time " value ", " price " and means "apparent value ". The name alludes to the fact that the yttrium contained in the mineral was mistaken for a new item.
Xenotime was first found in 1832 in the quarries at Hidra (about 10 km southwest of Flekkefjord ) in Norway. Xenotime - (Y) was first described by François Sulpice Beudant and xenotime - (Yb ) 1999 by Buck, Cooper, Cerny, Grice and Hawthorne.
Classification
Already in the now outdated but still in use 8th edition of the mineral classification by Strunz belonged xenotimes - (Y) and xenotime - (Yb ) to the mineral class of " phosphates, arsenates and vanadates " and then to the Department of " water clear phosphates without foreign anions " where they together with Chernovit - (Y), Pretulit, Wakefieldite - (Ce) and Wakefieldite - (Y) the " xenotime - group " with the system no. VII/A.14 formed.
The 9th edition used since 2001 and valid by the International Mineralogical Association (IMA ) of the Strunz'schen Mineral classification assigns xenotime - (Y) and xenotime - (Yb ) is also in the class of " phosphates, arsenates and vanadates " and there in the Department of " phosphates, etc. without additional anions, without H2O" one. This division, however, is further divided according to the size of the cations involved, so that the two minerals is "With only large cations " to find according to their composition in the subdivision where they also lend their names to " Xenotimgruppe " with the system no. 8.AD.35 and the other members Chernovit - (Y), Klinobisvanit, Dreyerit, Pretulit form Wakefieldite - (Ce), Wakefieldite - (La) and Wakefieldite - (Y).
The mainly common in English-speaking classification of minerals according to Dana assigns xenotime - (Y) and xenotime - (Yb ) in the class of " phosphates, arsenates and vanadates " and there in the department of " Anhydrous Phosphates, etc. " field. Here they are as Namensgebeber in the " xenotime group ( tetragonal: I41/amd ) " with the system no. 38.04.11. within the sub-division of " water clear phosphates, etc., A XO4 " to find.
Education and Locations
The xenotime minerals are formed either magmatic granites or pegmatites or hydrothermal veins in the mountains. After metamorphosis in gneisses and subsequent sedimentation xenotime is also found in placer deposits.
Locations include Brazil, Ichikawa in Japan, Madagascar, and Kragerö Hitterö in Norway, Ytterby in Sweden, and the United States.
Crystal structure
Xenotime - (Y ) crystallizes in the tetragonal space group I41/amd with the lattice parameters a = 6.89 Å and c = 6.04 Å and four formula units per unit cell.
Xenotime - (Yb ) also crystallizes in the tetragonal space group I41/amd with the lattice parameters a = 6.87 Å and c = 6.00 Å and four formula units per unit cell.