Monazite is a primarily reddish-brown phosphate mineral that contains rare-earth elements. Due to variability in composition, monazite is considered a group of minerals. The most common species of the group is monazite-(Ce), that is, the cerium-dominant member of the group. It occurs usually in small isolated crystals. It 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. There are five different most common species of monazite, depending on the relative amounts of the rare earth elements in the mineral:
The mineral bastnäsite (or bastnaesite) is one of a family of three carbonate-fluoride minerals, which includes bastnäsite-(Ce) with a formula of (Ce, La)CO3F, bastnäsite-(La) with a formula of (La, Ce)CO3F, and bastnäsite-(Y) with a formula of (Y, Ce)CO3F. Some of the bastnäsites contain OH− instead of F− and receive the name of hydroxylbastnasite. Most bastnäsite is bastnäsite-(Ce), and cerium is by far the most common of the rare earths in this class of minerals. Bastnäsite and the phosphate mineral monazite are the two largest sources of cerium and other rare-earth elements.
Fayalite is the iron-rich end-member of the olivine solid-solution series. In common with all minerals in the olivine group, fayalite crystallizes in the orthorhombic system with cell parameters a 4.82 Å, b 10.48 Å and c 6.09 Å.
Tephroite is the manganese endmember of the olivine group of nesosilicate minerals with the formula Mn2SiO4. A solid solution series exists between tephroite and its analogues, the group endmembers fayalite and forsterite. Divalent iron or magnesium may readily replace manganese in the olivine crystal structure.
Cerite is a complex silicate mineral group containing cerium, formula (Ce,La,Ca)
9(Mg,Fe3+
)(SiO
4)
6(SiO
3OH)(OH)
3. The cerium and lanthanum content varies with the Ce rich species and the La rich species. Analysis of a sample from the Mountain Pass carbonatite gave 35.05% Ce
2O
3 and 30.04% La
2O
3.
Libethenite is a rare copper phosphate hydroxide mineral. It forms striking, dark green orthorhombic crystals. It was discovered in 1823 in Ľubietová, Slovakia and is named after the German name of that locality (Libethen). Libethenite has also been found in the Miguel Vacas Mine, Conceição, Vila Viçosa, Évora District, Portugal, and in Tier des Carrières, Cahai, Vielsaim, Stavelot Massif, Luxembourg Province, Belgium.
Ancylite is a group of hydrous strontium carbonate minerals containing cerium, lanthanum and minor amounts of other rare-earth elements. The chemical formula is Sr(Ce,La)(CO3)2(OH)·H2O with ancylite-Ce enriched in cerium and ancylite-La in lanthanum.
Dollaseite-(Ce) is a sorosilicate end-member epidote rare-earth mineral which was discovered by Per Geijer (1927) in the Ostanmossa mine, Norberg district, Sweden. Dollaseite-(Ce), although not very well known, is part of a broad epidote group of minerals which are primarily silicates, the most abundant type of minerals on earth. Dollaseite-(Ce) forms as dark-brown subhedral crystals primarily in Swedish mines. With the ideal chemical formula, CaREE3+
Mg
2AlSi
3O
11,(OH)F, dollaseite-(Ce) can be partially identified by its content of the rare earth element cerium.
Stillwellite-(Ce) is a rare-earth boro-silicate mineral with chemical formula (Ce,La,Ca)BSiO5.
Corkite is a phosphate mineral in the beudantite subgroup of the alunite group. Corkite is the phosphate analogue of beudantite and with it, a complete solid solution range exists. Corkite will also form a solid solution with kintoreite.
Ferrokentbrooksite is a moderately rare mineral of the eudialyte group, with formula Na15Ca6(Fe,Mn)3Zr3NbSi25O73(O,OH,H2O)3(Cl,F,OH)2. The original formula was extended form to show the presence of cyclic silicate groups and presence of silicon at the M4 site, according to the nomenclature of eudialyte group. As suggested by its name, it is the (ferrous) iron analogue of kentbrooksite. When compared to the latter, it is also chlorine-dominant instead of being fluorine-dominant. The original (holotype) material is also relatively enriched in rare earth elements, including cerium and yttrium.
Johnsenite-(Ce) is a very rare mineral of the eudialyte group, with the chemical formula Na12(Ce,La,Sr,Ca,[ ])3Ca6Mn3Zr3WSi(Si9O27)2(Si3O9)2(CO3)O(OH,Cl)2. The original formula was extended to show the presence of both the cyclic silicate groups and silicon at the M4 site, according to the nomenclature of the eudialyte group. It is the third eudialyte-group mineral with essential tungsten, and second with essential rare earth elements. In fact, some niobium substitutes for tungsten in johnsenite-(Ce). Other characteristic feature is the presence of essential carbonate group, shared with carbokentbrooksite, golyshevite, mogovidite and zirsilite-(Ce).
Khomyakovite is an exceedingly rare mineral of the eudialyte group, with formula Na12Sr3Ca6Fe3Zr3W(Si25O73)(O,OH,H2O)3(OH,Cl)2. The original formula was extended to show the presence of both the cyclic silicate groups and M4-site silicon, according to the nomenclature of the eudialyte group. Some niobium substitutes for tungsten in khomyakovite. Khomyakovite is an iron-analogue of manganokhomyakovite, the second mineral being a bit more common. The two minerals are the only group representatives, beside taseqite, with species-defining strontium, although many other members display strontium diadochy. Khomyakovite is the third eudialyte-group mineral with essential tungsten.
Manganokhomyakovite is a very rare mineral of the eudialyte group, with the chemical formula Na12Sr3Ca6Mn3Zr3WSi(Si9O27)2(Si3O9)2O(O,OH,H2O)3(OH,Cl)2. This formula is in extended form, to show the presence of cyclic silicate groups and domination of silicon at the M4 site, basing on the nomenclature of the eudialyte group. Some niobium substitutes for tungsten in khomyakovite. As suggested by its name, manganokhomyakovite is a manganese-analogue of khomyakovite, the latter being more rare. The two minerals are the only group representatives, beside taseqite, with species-defining strontium, although many other members display strontium diadochy. Manganokhomyakovite is the third eudialyte-group mineral with essential tungsten.
Tistarite is an exceedingly rare mineral with the formula Ti2O3, thus being the natural analogue of titanium(III) oxide. In terms of chemistry it is the titanium-analogue of hematite, corundum, eskolaite, and karelianite. Other minerals with the general formula A2O3 are arsenolite, avicennite, claudetite, bismite, bixbyite, kangite, sphaerobismoite, yttriaite-(Y) and valentinite. Tistarite and grossmanite – both found in the famous Allende meteorite (so is kangite) – are the only currently known minerals with trivalent titanium. Titanium in minerals is almost exclusively tetravalent. The only known terrestrial occurrence of tistarite was found during minerals exploration by Shefa Yamim Ltd. in the upper mantle beneath Mount Carmel, Israel.
Yttriaite-(Y) is an exceedingly rare mineral, a natural form of yttrium oxide, Y2O3. In terms of chemistry it is yttrium-analogue of kangite, arsenolite, avicennite and senarmontite (isometric minerals). Other minerals with the general formula A2O3 include corundum, bismite, bixbyite, eskolaite, hematite, karelianite, sphaerobismoite, tistarite, and valentinite. Yttriaite-(Y) forms tiny inclusions in native tungsten.
Florencite-(Sm) is a very rare mineral of the plumbogummite group (alunite supergroup) with simplified formula SmAl3(PO4)2(OH)6. Samarium in florencite-(Sm) is substituted by other rare earth elements, mostly neodymium. It does not form separate crystals, but is found as zones in florencite-(Ce), which is cerium-dominant member of the plumbogummite group. Florencite-(Sm) is also a samarium-analogue of florencite-(La) (lanthanum-dominant) and waylandite (bismuth-dominant), both being aluminium-rich minerals.
Monazite-(La) is a relatively rare representative of the monazite group, with lanthanum being the dominant rare earth element in its structure. As such, it is the lanthanum analogue of monazite-(Ce), monazite-(Nd), and monazite-(Sm). It is also the phosphorus analogue of gasparite-(La). The group contains simple rare earth phosphate minerals with the general formula of ATO4, where A = Ce, La, Nd, or Sm (or, rarely, Bi), and B = P or, rarely, As. The A site may also bear Ca and Th.
Monazite-(Nd) is a relatively rare representative of the monazite group, with neodymium being the dominant rare earth element in its structure. This variety of monazite is typically colored bright rose-red. It is the neodymium analogue of monazite-(Ce), monazite-(La), and monazite-(Sm). The group contains simple rare earth phosphate minerals with the general formula of ATO4, where A = Ce, La, Nd, or Sm (or, rarely, Bi), and B = P or, rarely, As. The A site may also bear Ca and Th.
Monazite-(Sm) is an exceedingly rare representative of the monazite group, with samarium being the dominant rare earth element in its structure. It is the samarium analogue of monazite-(Ce), monazite-(La), and monazite-(Nd). It is only the second known mineral with samarium being the mineral-forming element, after florencite-(Sm). The group contains simple rare earth phosphate minerals with the general formula of ATO4, where A = Ce, La, Nd, or Sm (or, rarely, Bi), and B = P or, rarely, As. The A site may also bear Ca and Th.
