21 Photos
Bastnaesite
Chemical Formula	(Ce,La,Y)CO3F
Species	Carbonates
Crystal System	Hexagonal
Mohs Scale	4-5
Specific Gravity	4.95-5.0
Color	Honey-yellow, reddish brown
Streak	White
Luster	Vitreous, greasy, pearly on basal partings
Refractive Index	nω = 1.717–1.722nε = 1.818–1.823
Diaphaneity	Transparent to translucent
Cleavage	Imperfect to indistinct on , parting on
Fracture	Uneven
Crystal Habit：Tabular to equant striated crystals, also granular, massive

The mineral bastn?site (or bastnaesite) is one of a family of three carbonate-fluoride minerals, which includes bastn?site-(Ce) with a formula of (Ce, La)CO₃F, bastn?site-(La) with a formula of (La, Ce)CO₃F, and bastn?site-(Y) with a formula of (Y, Ce)CO₃F. Most bastn?site is bastn?site-(Ce), and cerium is by far the most common of the rare earths in this class of minerals. Bastn?site and the phosphate mineral monazite are the two largest sources of cerium and other rare earth elements.

Bastn?site was first described by the Swedish chemist Wilhelm Hisinger in 1838. It is named for the Bastn?s mine near Riddarhyttan, V?stmanland, Sweden. Bastn?site also occurs as very high quality specimens at the Zagi Mountains, Pakistan. Bastn?site occurs in alkali granite and syenite and in associated pegmatites. It also occurs in carbonatites and in associated fenites and other metasomatites.

Composition

Bastn?site has cerium, lanthanum and yttrium in its generalized formula but officially the mineral is divided into three minerals based on the predominant rare earth element. There is bastn?site-(Ce) with a more accurate formula of (Ce, La)CO₃F. There is also bastn?site-(La) with a formula of (La, Ce)CO₃F. And finally there is bastn?site-(Y) with a formula of (Y, Ce)CO₃F. There is little difference in the three in terms of physical properties and most bastn?site is bastn?site-(Ce). Cerium in most natural bastn?sites usually dominates the others. Bastn?site and the phosphate mineral monazite are the two largest sources of cerium, an important industrial metal.

Bastn?site is closely related to the mineral series parisite. The two are both rare earth fluorocarbonates, but parisite's formula of Ca(Ce, La, Nd)₂(CO₃)₃F₂ contains calcium (and a small amount of neodymium) and a different ratio of constituent ions. Parisite could be viewed as a molecule of calcite (CaCO₃) added to two molecules of bastn?site. In fact, the two have been shown to alter back and forth with the addition or loss of CaCO₃ in natural environments.^{[citation needed]}

Bastn?site forms a series with the minerals hydroxylbastnasite-(Ce) and hydroxylbas?nasite-(Nd). The three are members of a substitution series that involves the possible substitution of fluorine ions for hydroxyl (OH) ion groups. Hydroxylbastnasite-(Ce) has a formula of (Ce,La)CO₃(OH,F).

Name

Bastn?site gets its name from its type locality, the Bastn?s Mine, Riddarhyttan, V?stmanland, Sweden. Ore from the Bastn?s Mine led to the discovery of several new minerals and chemical elements by Swedish scientists such as J?ns Jakob Berzelius, Wilhelm Hisinger and Carl Gustav Mosander. Among these are the chemical elements cerium, which was described by Hisinger in 1803, and lanthanum in 1839. Hisinger, who was also the owner of the Bastn?s mine, chose to name one of the new minerals bastn?sit when it was first described by him in 1838.

Occurrence

Although a scarce mineral and never in great concentrations, it is widespread, and one of the more common rare-earth carbonates. Bastn?site has been found in karst bauxite deposits in Hungary, Greece and the Balkans region. Also found in carbonatites, a rare carbonate igneous intrusive rock, at Fen, Norway; Bayan Obo, Mongolia; Kangankunde, Malawi; Kizilcaoren, Turkey and the Mountain Pass rare earth mine in California, USA. At Mountain Pass, bastn?site is the leading ore mineral. Some bastn?site has been found in the unusual granites of the Langesundsfjord area, Norway; Kola Peninsula, Russia; Mont Saint-Hilaire mines, Ontario, and Thor Lake deposits, Northwest Territories, Canada. Hydrothermal sources have also been reported.

Mining history

In 1949, the huge carbonatite-hosted bastn?site deposit was discovered at Mountain Pass, San Bernardino County, California. This discovery alerted geologists as the existence of a whole new class of rare earth deposit: the rare earth containing carbonatite. Other examples were soon recognized, particularly in Africa and China. The exploitation of this deposit began in the mid-1960s after it had been purchased by Molycorp (Molybdenum Corporation of America). The lanthanide composition of the ore included 0.1% europium oxide, which was sorely needed by the burgeoning color television industry, to provide the red phosphor, so as to maximize picture brightness. The composition of the lanthanides was about 49% cerium, 33% lanthanum, 12% neodymium, and 5% praseodymium, with some samarium and gadolinium, or distinctly more lanthanum and less neodymium and heavies as compared to commercial monazite. However, the europium content was at least double that of a typical monazite. Mountain Pass bastn?site was the world's major source of lanthanides from the 1960s to the 1980s. Thereafter, China became increasingly important to world rare earth supply. Chinese deposits of bastn?site include several in Sichuan Province, and the massive deposit at Bayan Obo, Inner Mongolia, which had been discovered early in the 20th century, but not exploited until much later. Bayan Obo is currently (2008) providing the majority of the world's lanthanides. Bayan Obo bastn?site occurs in association with monazite (plus enough magnetite to sustain one of the largest steel mills in China), and unlike carbonatite bastn?sites, is relatively closer to monazite lanthanide compositions, with the exception of its generous 0.2% content of europium.^{[citation needed]}

Ore technology

At Mountain Pass, bastn?site ore was finely ground, and subjected to flotation to separate the bulk of the bastn?site from the accompanying barite, calcite, and dolomite. Marketable products include each of the major intermediates of the ore dressing process: flotation concentrate, acid-washed flotation concentrate, calcined acid washed bastn?site, and finally a cerium concentrate, which was the insoluble residue left after the calcined bastn?site had been leached with hydrochloric acid. The lanthanides that dissolved as a result of the acid treatment were subjected to solvent extraction, to capture the europium, and purify the other individual components of the ore. A further product included a lanthanide mix, depleted of much of the cerium, and essentially all of samarium and heavier lanthanides. The calcination of bastn?site had driven off the carbon dioxide content, leaving an oxide-fluoride, in which the cerium content had become oxidized to the less basic quadrivalent state. However, the high temperature of the calcination gave less-reactive oxide, and the use of hydrochloric acid, which can cause reduction of quadrivalent cerium, led to an incomplete separation of cerium and the trivalent lanthanides. By contrast, in China, processing of bastn?site, after concentration, starts with heating with sulfuric acid.^{[citation needed]}