Actinide minerals, or actinides, are those with unusually high concentrations, atomic per cents, or weight per cents, of the actinide elements, group 3: actinium (Ac) through lawrencium (Lr).

Umbozerite (red arrow) is from Karnasurt Mt., Lovozero Massif, Kola, Russia. Credit: Weirdmeister.{{free media}}




This monazite is a tabular crystal from Rostadheia, Iveland, Norway. Credit: Aangelo.{{free media}}
The primary source of the world's thorium is the rare-earth-and-thorium-phosphate mineral monazite. Credit: USGS.{{free media}}
Monazite gets its name from the Greek word "monazein", which means "to be alone", in allusion to its isolated crystals and their rarity when first found. Credit: Robert M. Lavinsky.{{free media}}

Monazite, a primarily reddish-brown phosphate mineral that contains rare-earth elements, with variability composition, is considered a group of minerals:[1]

  • monazite-(Ce), (Ce,La,Nd,Th)PO
    (the most common member),
  • monazite-(La), (La,Ce,Nd)PO
  • monazite-(Nd), (Nd,La,Ce)PO
  • monazite-(Sm), (Sm,Gd,Ce,Th)PO
  • monazite-(Pr), (Pr,Ce,Nd,Th)PO

occurs usually in small isolated crystals has a hardness of 5.0 to 5.5 on the Mohs scale of mineral hardness and is relatively dense, about 4.6 to 5.7 g/cm3.

The primary source of the world's thorium is the rare-earth, and thorium, phosphate mineral monazite.

Silica (SiO
) is present in trace amounts, as is small amounts of uranium.

Due to the alpha decay of thorium and uranium, monazite contains a significant amount of helium, which can be extracted by heating.[2]


This specimen of thorianite is from th Ambatofotsy pegmatite in Madagascar. Credit: Robert Lavinsky.{{free media}}

"Thorianite is a rare thorium oxide mineral, ThO2.[3] ... [It has a] high percentage of thorium; it also contains the oxides of uranium, lanthanum, cerium, praseodymium and neodymium. ... the mineral is slightly less radioactive than pitchblende, but is harder to shield due to its high energy gamma rays. It is common in the alluvial gem-gravels of Sri Lanka, where it occurs mostly as water worn, small, heavy, black, cubic crystals."[4]


Thorite is from Kemp prospect (Kemp property; Kemp uranium mine), Cardiff Township, Haliburton County, Ontario, Canada. Credit: Rob Lavinsky.{{free media}}

Thorite has the formula ThSiO4.

Thorite occurs "widespread as a primary mineral chiefly in pegmatites, metasomatized zones in impure limestones, hydrothermal veins, and in detrital deposits."[5]


Umbozerite is from Karnasurt Mt., Lovozero Massif, Kola, Russia, size 4.2 cm. Credit: Weirdmeister.{{free media}}

The IMA-CNMNC approved mineral symbol is Ubz.[6]

Umbozerites have the chemical formula Na
, IMA formula Na
, common impurities: Ti,Ce,Fe,U,Mn,Ca,Ba,K, and Crystal System: Amorphous.[7]

Environment: In ussingite veinlets cutting alkalic rocks, type locality: Umbozero (Lake Umba), Kola Peninsula, Russia, dark brown prismatic umbozerite masses in pegmatite rock, Metamict - Mineral originally crystalline, now amorphous due to radiation damage, Pseudo Tetragonal - Crystals show a tetragonal shape, Umbozerite is Radioactive as defined in 49 CFR 173.403, greater than 70 Bq / gram.[8]

Occurrence: In pneumatolytic-hydrothermal veins cutting alkalic rocks in the upper part of a differentiated alkalic massif, Crystal Data: Metamict; tetragonal after recrystallization[9]

Association: Ussingite, sphalerite, belovite, manganoan pectolite, lorenzenite, niobium-bearing minerals of the lomonosovite group.[9]

Distribution: Found on Mts. Karnasurt and Punkaruaiv, near Lake Umba, Lovozero massif, Kola Peninsula, Russia.[9]


Xenotime is with rutile. Credit: Robert M. Lavinsky.{{free media}}

Xenotime is a rare-earth (Dy,Er,Tb,Yb) and actininde metals (Th,U) phosphate mineral, all as secondary components replacing yttrium the major component of the orthophosphate (YPO
), which also forms a solid solution series with chernovite-(Y) (YAsO
) and may contain trace impurities of arsenic, silicon dioxide and calcium. Due to uranium and thorium impurities, some xenotime specimens may be weakly to strongly radioactive. Lithiophyllite, monazite and purpurite are sometimes grouped with xenotime in the informal "anhydrous phosphates" group. Xenotime is used chiefly as a source of yttrium and heavy lanthanide metals (dysprosium, ytterbium, erbium and gadolinium).

The image on the right contains shockingly large and well-developed xenotime crystal with unusually good lustre, rich chocolate color, and unusually equant crystalllographic form. This crystal is complete all around, 360 degrees, with inclusions of golden rutile in the xenotime, included 0.1 to 1 mm below the surface under a thin translucent layer of xenotime.

Occurrences: As a minor accessory mineral, found in pegmatites and other igneous rocks, gneisses rich in mica and quartz.

Associations: biotite and other micas, chlorite group minerals, quartz, zircon, certain feldspars, analcime, anatase, brookite, rutile, siderite and apatite, diagenetic as minute grains or as extremely thin (less than 10 µ) coatings on detrital zircon grains in siliciclastic sedimentary rocks.[10]




Autunite is from the Daybreak Mine, Washington. Credit: Robert M. Lavinsky.{{free media}}
free media
This gamma-ray spectrum contains the typical isotopes of the uranium-radium decay line. Credit: Wusel007.{{free media}}

Autinite has the chemical formula Ca(UO

Autunite (hydrated calcium uranyl phosphate) is a yellow-greenish fluorescent phosphate mineral with a Mohs hardness of 2–​2 12.[11][12] Autunite crystallizes in the orthorhombic system and often occurs as tabular square crystals, commonly in small crusts or in fan-like masses. Due to the moderate uranium content of 48.27% it is radioactive and also used as uranium ore. Autunite fluoresces bright green to lime green under UV light. The mineral is also called calco-uranite, but this name is rarely used and effectively outdated.[13]

Autunite was discovered in 1852 near Autun, France, which is also autunite's namesake, occurs as an oxidation product of uranium minerals in granite pegmatites and hydrothermal deposits, with associate minerals: metaautunite, torbernite, phosphuranylite, saleeite, uranophane and sabugalite.[14]

Autunite was found inside the Daybreak Mine on Mount Kit Carson, Spokane, Washington (or sometimes referred to as "near Mount Spokane"), in "vugs, fractures, and shear zones in granitic rock", that showed signs of another phosphate, apatite, which may have helped lead to the formation of autunite, by providing a source of phosphate and lime, where the formation may have occurred with the interaction of uranium leached from a separate deposit.[15]

Elements usually emit a gamma-ray during nuclear decay or fission. The gamma-ray spectrum at right shows typical peaks for 226
, 214
, and 214
. These isotopes are part of the uranium-radium decay line. As 238
is an alpha-ray emitter, it is not shown. The peak at 40 keV is not from the mineral. From the color of the rock shown the yellowish mineral is likely to be autunite.


The Carnotite is from the Happy Jack Mine, Utah. Credit: USGS.{{free media}}
Carnotite occurs on fossilized wood - Locality: St. George, Utah - Exhibited in the Mineralogical Museum, Bonn, Germany. Credit: Ra'ike.{{free media}}

Carnotite is a potassium uranium vanadate radioactive mineral with chemical formula: K
.[16] The water content can vary and small amounts of calcium, barium, magnesium, iron, and sodium are often present. Carnotite is a bright yellow to greenish yellow mineral[16] that occurs typically as crusts and flakes in sandstones. Amounts as low as one percent will color the sandstone a bright yellow. The high uranium content makes carnotite an important uranium ore and also radioactive. It is a secondary vanadium and uranium mineral usually found in sedimentary rocks in arid climates. It is an important ore of uranium in the Colorado Plateau region of the United States where it occurs as disseminations in sandstone[17] and concentrations around petrified logs.


"An excess of U234 is detected in some endogenic minerals."[18]

The presence of U234 suggests "an intensive uranium migration in the zone of epigenesis. A measurable U235 excess may accumulate as a result of the decay of some transuranium isotope, being present in the mineral. The surplus content of U235 in magnetites of a pegmatite vein by 45 plus or minus 5 and 23 plus or minus 6 percent is confirmed. The other minerals of this ore body have a normal isotopic composition which indicates the local presence of [a] transuranium emitter in the magnetite. An excess of actinium (and U234) is also found in this mineral."[18]


This is an image of the mineral pitchblende, or uraninite. Credit: Geomartin.{{free media}}
These crystals are uraninite from Trebilcock Pit, Topsham, Maine. Credit: Robert Lavinsky.{{free media}}

"Uraninite is a radioactive, uranium-rich mineral and ore with a chemical composition that is largely UO2, but also contains UO3 and oxides of lead, thorium, and rare earth elements. It is most commonly known as pitchblende (from pitch, because of its black color ... All uraninite minerals contain a small amount of radium as a radioactive decay product of uranium. Uraninite also always contains small amounts of the lead isotopes 206Pb and 207Pb, the end products of the decay series of the uranium isotopes 238U and 235U respectively. ... The extremely rare element technetium can be found in uraninite in very small quantities (about 0.2 ng/kg), produced by the spontaneous fission of uranium-238."[19]

The image at left shows well-formed crystals of uraninite. The image at right shows botryoidal unraninite. Because of the uranium decay products, both sources are gamma-ray emitters.


Torbernitte is a hydrated green copper uranyl phosphate mineral. Credit: Didier Descouens.{{free media}}

Torbernite is a radioactive, hydrated green copper uranyl phosphate mineral, found in granites and other uranium-bearing deposits as a secondary mineral. Torbernite is isostructural with the related uranium mineral, autunite. The chemical formula of torbenite is similar to that of autunite in which a Cu2+ cation replaces a Ca2+. The number of water hydration molecules can vary between 12 and 8, giving rise to the variety of metatorbernite when torbernite spontaneously dehydrates. Torbernite has the chemical formula Cu(UO
• 12H


The rarest naturally occurring element on Earth is named Astatine and it occurs in uraninite as a uranium decay product. Credit: Fred E. Davis.{{fairuse}}
A cluster of seven crystals, four are visible, in the photo of uraninite, with a yellow uranophane coating. Credit: Fred E. Davis.{{fairuse}}

All of the known isotopes of astatine are very short-lived. Astatine occurs naturally in minerals such as uraninite as a decay product of uranium.


Uranophane is a calcium uranium silicate hydrate mineral. Credit: United States Geological Survey.{{free media}}

"Uranophane Ca(UO2)2(SiO3OH)2·5H2O is a rare calcium uranium [nesosilicate] hydrate mineral that forms from the oxidation of uranium bearing minerals. Uranophane is also known as uranotile. It has a yellow color and is radioactive."[21]



  1. Minerals containing actinide elements should be closer to the center of the Earth than those high in the much lighter elements.

See alsoEdit


  1. Monazite group on Mindat.org
  2. "Helium From Sand", March 1931, Popular Mechanics p. 460.
  3. C. Frondel (1958). Systematic Mineralogy of Uranium and Thorium. United States Government Printing Office. 
  4. "Thorianite, In: Wikipedia". San Francisco, California: Wikimedia Foundation, Inc. February 27, 2013. Retrieved 2013-05-08.
  5. Willard Lincoln Roberts; George Robert Rapp Jr.; Julius Weber (1974). Encyclopedia of Minerals. New York, New York, USA: Van Nostrand Reinhold Company. pp. 693. ISBN 0-442-26820-3. 
  6. Warr, L.N. (2021). IMA–CNMNC approved mineral symbols. Mineralogical Magazine, 85(3), 291-320. doi:10.1180/mgm.2021.43
  7. "Umbozerite". Retrieved 19 November 2021.
  8. "Umbozerite Mineral Data". Retrieved 19 November 2021.
  9. 9.0 9.1 9.2 "Umbozerite" (PDF). Retrieved 19 November 2021.
  10. Daniela Vallini. "Travel Report on Xenotime geochronology". Retrieved January 8, 2006.
  11. Barthelmy, Dave. "Autunite Mineral Data". webmineral.com. Retrieved 2018-01-26.
  12. "Autunite: Autunite mineral information and data". www.mindat.org. Retrieved 2018-04-28.
  13. Autunite, In: Encyclopædia Britannica. 03 (11th ed.). 1911. 
  14. Handbook of Mineralogy
  15. G. W. Leo (1960). Autunite from Mt. Spokane, Washington. U.S. Geologic Survey, Menlo Park, California: The American Mineralogist. pp. 1. 
  16. 16.0 16.1 [1] Carnotite, accessdate 19 November 2021
  17. [2] Carnotite
  18. 18.0 18.1 Cherdyntsev, V.V.; Orlov, D.P.; Isabaev, E.A.; Ivanov, V.I. (01 January 1961). "Isotopes of Uranium in Natural Conditions. II. Isotopic Composition of Uranium of Minerals". Geokhimiya (U.S.S.R.) (in Russian). http://www.osti.gov/scitech/biblio/4818910. Retrieved 2015-04-04. 
  19. "Uraninite, In: Wikipedia". San Francisco, California: Wikimedia Foundation, Inc. April 20, 2013. Retrieved 2013-05-08.
  20. [3] Torbernite
  21. "Uranophane, In: Wikipedia". San Francisco, California: Wikimedia Foundation, Inc. February 28, 2013. Retrieved 2013-05-08.

External linksEdit