# Minerals/Actinides

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).

## Monazites

Monazite, a primarily reddish-brown phosphate mineral that contains rare-earth elements, with variability composition, is considered a group of minerals:
* monazite-(Ce), (Ce,La,Nd,Th)PO $_4$ (the most common member),
* monazite-(La), (La,Ce,Nd)PO $_4$,
* monazite-(Nd), (Nd,La,Ce)PO $_4$,
* monazite-(Sm), (Sm,Gd,Ce,Th)PO $_4$,
* monazite-(Pr), (Pr,Ce,Nd,Th)PO $_4$.
(Ce,La,Nd,Th)PO $_4$ 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/cm$^3$.
The primary source of the world's thorium is the rare-earth, and thorium, phosphate mineral monazite.
Silica (SiO $_2$) 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.

## Thorianites

"Thorianite is a rare thorium oxide mineral, ThO$_2$. ... [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."

## Thorites

Thorite has the formula ThSiO$_4$.
Thorite occurs "widespread as a primary mineral chiefly in pegmatites, metasomatized zones in impure limestones, hydrothermal veins, and in detrital deposits."

## Umbozerites

The IMA-CNMNC approved mineral symbol is Ubz.
Umbozerites have the chemical formula Na $_3$Sr $_4$Th[Si(O,OH $_{(3-4)}$] $_8$, IMA formula Na $_3$Sr $_4$ThSi $_8$(O,OH) $_{24}$, common impurities: Ti,Ce,Fe,U,Mn,Ca,Ba,K, and Crystal System: Amorphous.
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.
Occurrence: In pneumatolytic-hydrothermal veins cutting alkalic rocks in the upper part of a differentiated alkalic massif, Crystal Data: Metamict; tetragonal after recrystallization
Association: Ussingite, sphalerite, belovite, manganoan pectolite, lorenzenite, niobium-bearing minerals of the lomonosovite group.
Distribution: Found on Mts. Karnasurt and Punkaruaiv, near Lake Umba, Lovozero massif, Kola Peninsula, Russia.

## Xenotimes

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 $_4$), which also forms a solid solution series with chernovite-(Y) (YAsO $_4$) 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.

## Autunites

[[Image:Autunite-rl-aut8a.jpg|thumb|left|thumb|224x224px|Autunite is from Mount Kit Carson, Washington. Credit: Robert M. Lavinsky.{{tlx|free media]]
Autinite has the chemical formula Ca(UO $_2$) $_2$(PO $_4$) $_2$·10–12H $_2$O.
Autunite (hydrated calcium uranyl phosphate) is a yellow-greenish fluorescent phosphate mineral with a Mohs hardness of 2–​2 $^1$⁄$_2$. 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.
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.
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.
Elements usually emit a gamma-ray during nuclear decay or fission. The gamma-ray spectrum at right shows typical peaks for $^{226}$ Ra, $^{214}$ Pb, and $^{214}$ Bi. These isotopes are part of the uranium-radium decay line. As $^{238}$ U 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.

## Carnotites

Carnotite is a potassium uranium vanadate radioactive mineral with chemical formula: K $_2$(UO $_2$) $_2$(VO $_4$) $_2$·3H $_2$O. 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 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 and concentrations around petrified logs.

## Magnetites

"An excess of U$^{234}$ is detected in some endogenic minerals."
The presence of U$^{234}$ suggests "an intensive uranium migration in the zone of epigenesis. A measurable U$^{235}$ excess may accumulate as a result of the decay of some transuranium isotope, being present in the mineral. The surplus content of U$^{235}$ 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 U$^{234}$) is also found in this mineral."

## Pitchblendes

"Uraninite is a radioactive, uranium-rich mineral and ore with a chemical composition that is largely UO$_2$, but also contains UO$_3$ 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 $^{206}$Pb and $^{207}$Pb, the end products of the decay series of the uranium isotopes $^{238}$U and $^{235}$U 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."
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.

## Torbernites

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 Cu$^{2+}$ cation replaces a Ca$^{2+}$. 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 $_2$) $_2$(PO $_4$) $_2$ • 12H $_2$O.

## Uraninites

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.

## Uranophanes

"Uranophane Ca(UO$_2$)$_2$(SiO$_3$OH)$_2$·5H$_2$O 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."

## Hypotheses

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