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(Ca,Ce,La,Y)2(Al,Fe)3Si3O12(OH) Monoclinic mineral distinguished from all other members of the epidote group of silicates by a relatively high content of rare earths. Also known as bucklandite; cerine; orthite; treanorite.



(named after the British mineralogist T. Allan), also orthite, a mineral of the epidote group. Allanite is characterized by its pitch-black or greenish brown color and its vitreous luster. The mineral’s approximate formula is (Ca, Ce, Mn)2-(Fe2+, Fe3+, Mg) Al2[SiO4][Si2O7]O(OH). Allanite contains up to 6 percent Ce2O3 and frequent admixtures of Th and U; it sometimes contains up to 8 percent Y2O3. Hydrous varieties, which have become metamict, also exist.

Allanite generally crystallizes in the monoclinic system, forming slender prismatic crystals. It also may occur as irregular aggregates or grains. The mineral is brittle and has a hardness on Mohs’ scale of 6 and a density of 4,100 kg/m3 (reduced to 2,700 kg/m3 in converted varieties). Allanite is radioactive. The mineral occurs rarely in natural form but is usually found in association with other minerals in pegmatite veins. It also occurs in the form of individual crystals in granites. Allanite is valuable in the extraction of such rare-earth elements as Ce and Y.

References in periodicals archive ?
They display a fairly uniform modal composition and consist of feldspar, quartz, amphibole, clinopyroxene, and small quantities of opaque oxide, titanite, allanite, and rare epidote, tourmaline and (?
Summary of the activity per unit mass measured for the different radionuclides that constitute the smaller measured NORM samples Sample Radionuclide Activity (Bq/kg) Uncertainty (%) Allanite K-40 1397 35 Ra-226 1155 35 Th-232 17855 30 U-238 2178 35 Monozite Ra-226 24740 25 Th-232 170903 25 Pyrochlore Ra-226 1836 40 Th-232 35303 30 U-238 7833 35 Zircon Ra-226 232 40 Th-232 14 45 U-238 219 40 ISG Pye Ra-226 67 26 Th-232 54 42 K-40 151 48 DAP Ra-226 15 29 Th-232 10 34 U-238 1923 35 K-40 6 30 CEMEX Ra-226 57 28 type FC Th-232 39 27 U-238 139 48 K-40 60 30 Monocalcium Ra-226 16 23 phosphate (biofos) Th-232 11 43 U-238 1970 31 K-40 6 29 Australian Ra-226 1963 37 zircon sand Th-232 442 33 U-238 3179 39
Epidote is frequent in the foliated matrix and occasionally formed around allanite that is probably of igneous origin.
Typical accessory minerals include apatite, zircon, fluorite, magnetite, titanite, and allanite.
Accessory minerals are apatite, zircon, ilmenite, rarely magmatic andalusite, cordierite, monazite, xenotime and allanite.
Schlieren consists of biotite, amphibole, zircon, allanite, monazite, magnetite, and fluorite.
The mineral constituents are K-feldspar (microperthite), plagioclase, quartz, riebekite, hornblende, aegirine-augite, biotite, apatite, zircon, allanite, titanite, epidote, rutile and magnetite.
Allanite is the host rare earth minerai and occurs mainly as finely disseminated grains throughout the rock.
Accessory minerals are sometimes very abundant ilmenite, less abundantly by apatite, rutile and zircon and very rare allanite.
The REEs at Hoidas Lake are hosted in the phosphate mineral apatite and the silicate mineral allanite.
Allanite, sphene and leucoxene occur as minor accessories along with local epidote (Jan et al.
The NYF Mukinbudin pegmatite field has been known for rare minerals including allanite, euxenite, fergusonite, ilmenorutile, monazite, xenotime and zircon since 2000.