Dollaseite-(Ce) is a

sorosilicate Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust. In mineralogy, silica (silicon dioxide, ) is usually consid ...

end-member

epidote Epidote is a calcium aluminium iron sorosilicate mineral. Description Well developed crystals of epidote, Ca2Al2(Fe3+;Al)(SiO4)(Si2O7)O(OH), crystallizing in the monoclinic system, are of frequent occurrence: they are commonly prismatic in hab ...

rare-earth mineral A rare-earth mineral contains one or more rare-earth elements as major metal constituents. Rare-earth minerals are usually found in association with alkaline to peralkaline igneous complexes, in pegmatites associated with alkaline magmas and in ...

which was discovered by

Per Geijer Per Adolf Geijer (born 7 May 1886 in Svealand, died 18 April 1976 in Danderyd) was a Swedish geologist, mineralogist, and professor. He was a member of the Geijer family (son of Gottschalk Geijer, grandson of Per Adolf Geijer and grandfather ...

(1927) in the Ostanmossa mine (Östanmossa gruva), Norberg district,

Sweden Sweden, formally the Kingdom of Sweden,The United Nations Group of Experts on Geographical Names states that the country's formal name is the Kingdom of SwedenUNGEGN World Geographical Names, Sweden./ref> is a Nordic country located on ...

. Dollaseite-(Ce), although not very well known, is part of a broad epidote group of minerals which are primarily

silicates In chemistry, a silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name i ...

, 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, , dollaseite-(Ce) can be partially identified by its content of the

rare earth element The rare-earth elements (REE), also called the rare-earth metals or (in context) rare-earth oxides or sometimes the lanthanides (yttrium and scandium are usually included as rare earths), are a set of 17 nearly-indistinguishable lustrous silve ...

cerium Cerium is a chemical element with the symbol Ce and atomic number 58. Cerium is a soft, ductile, and silvery-white metal that tarnishes when exposed to air. Cerium is the second element in the lanthanide series, and while it often shows the +3 o ...

History

The mineral provisionally named "magnesium orthite" by Geijer himself was renamed after structural refinement by Peacor and Dunn in 1988 led to its proper classification. The name dollaseite-(Ce) was chosen in honor of Wayne Dollase, who performed broad research on epidote minerals. The original confusion of the mineral's composition was because of a complex atomic composition where an exchange of cations leads to a form of dollaseite-(Ce) that at first glimpse resembles an Mg analogue of

allanite Allanite (also called orthite) is a sorosilicate group of minerals within the broader epidote group that contain a significant amount of rare-earth elements. The mineral occurs mainly in metamorphosed clay-rich sediments and felsic igneous rocks ...

, now known as dissakisite-(Ce). Enami and Zang, Meyer, Hanson and Pearce also reported minerals that resembled the composition of a Mg analogue of allanite but none had sufficient data, or exact composition to be declared as a Mg analogue of allanite. It was not until 1991 that Edward S. Grew established dissakisite as the actual Mg-dominant allanite mineral with formula .Grew, E.S., Essene, E.J., Peacor D.R., Su, S. and Asami, M. (1991) Dissakisite-(Ce), a new member of the epidote group and the Mg analogue of allanite-(Ce), from Antarctica, American Mineralogist, 76, 1990-1997

Composition

With a general formula for the

group of A₂M₃Si₃O₁₃HDollase, W.A. (1971) Refinement of the crystal structures of Epidote, Allanite and Hancockite. American Mineralogist, 56, 447-464 dollaseite-(Ce) received its formula of based on data from

electron microprobe An electron microprobe (EMP), also known as an electron probe microanalyzer (EPMA) or electron micro probe analyzer (EMPA), is an analytical tool used to non-destructively determine the chemical composition of small volumes of solid materials. It ...

analytical procedures. The results give the empirical formula (Ca_.91 Ce_.45 La_.20 Nd_.20 Pr_.09 Sm_.08 Gd_.06)(Mg_1.81 Fe_.25)Al_.97 Si_3.0(OH)_1.25 F_.88 O_10.99 from which the standard formula is then derived after applying Levinson’s rules for renaming REE minerals.Peacor, D.R. and Dunn P.J. (1988) Dollaseite-(Ce)(magnesium orthite redefined): Structure refinement and implications for F + M2+ substitutions in epidote-group minerals, American Mineralogist, 73, 838-842

Structure

The atomic structure of dollaseite-(Ce) can be somewhat complex at times due to the charge-

coupled substitution Coupled substitution is the geological process by which two elements simultaneous substitute into a crystal in order to maintain overall electrical neutrality and keep the charge constant. In forming a solid solution series, ionic size is more ...

involving both cations and anions: + = + .Holtstam, D. and Andersson, U.B. (2007) The REE minerals of the Bastanas-type deposits, South-Central Sweden, The Canadian Mineralogist, 45, 1073-1114 The average epidote-group mineral’s structure has chains of edge-sharing octahedral such as Al³⁺, Fe³⁺, Mn³⁺. The cavities that are formed by the octahedral chains that are occupied by A(1) and A(2) cationsDollase, W.A. (1969) Refinement and comparison of the structures of Zoisite and Clinozoisite. American Mineralogist, 53, 1882-1898 are occupied by Ca²⁺ and its REE, Ce³⁺. Like the rest of the members of the epidote group, the aluminium octahedra in dollaseite-(Ce) share edges, forming endless chains.Dollase, W.A. (1968) Crystal structure and cation ordering of piemontite. American Mineralogist, 54, 710-717 Similar to the other epidote-group minerals, dollaseite-(Ce) is

monoclinic In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in the orthorhombic s ...

and thus is part of the

space group In mathematics, physics and chemistry, a space group is the symmetry group of an object in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of an object that leave it unch ...

P2₁/m.Armbruster, T. (2006) Recommended nomenclature of epidote-group minerals. European Mineralogical Journals, 18 551-567 Peacor and Dunn (1988) refined the lattice parameters of dollaseite-(Ce) and concluded that the

parameters A parameter (), generally, is any characteristic that can help in defining or classifying a particular system (meaning an event, project, object, situation, etc.). That is, a parameter is an element of a system that is useful, or critical, when ...

were a=8.934(18) Å, b=5.721(7) Å, c=10.176(22) Å.

Geologic occurrence

Dollaseite-(Ce) can generally be found in mineralized

dolomite Dolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincor ...

tremolite Tremolite is a member of the amphibole group of silicate minerals with composition: Ca2(Mg5.0-4.5Fe2+0.0-0.5)Si8O22(OH)2. Tremolite forms by metamorphism of sediments rich in dolomite and quartz. Tremolite forms a series with actinolite and fer ...

rocks in the form of dark brown and subhedral crystals. Dollaseite-(Ce) can occur in a number of locations, but the most prominent is at Östanmossa, Sweden. The type of dollaseite-(Ce) that can generally be found at this location tends to be

iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in fr ...

-poor and occurs in

skarn Skarns or tactites are hard, coarse-grained metamorphic rocks that form by a process called metasomatism. Skarns tend to be rich in calcium-magnesium-iron-manganese-aluminium silicate minerals, which are also referred to as calc-silicate minerals ...

. The fact that dollaseite-(Ce) can be prominently found in Sweden comes as no surprise since Sweden has been known to host many REE epidote-group minerals such as dissakisite-(Ce) and allanite-(Ce). Another dollaseite-(Ce) specimen with composition slightly similar to that of dissakisite-(Ce) can be found in rock composed of

fluorite Fluorite (also called fluorspar) is the mineral form of calcium fluoride, CaF2. It belongs to the halide minerals. It crystallizes in isometric cubic habit, although octahedral and more complex isometric forms are not uncommon. The Mohs scale ...

and fluorian

phlogopite Phlogopite is a yellow, greenish, or reddish-brown member of the mica family of phyllosilicates. It is also known as magnesium mica. Phlogopite is the magnesium endmember of the biotite solid solution series, with the chemical formula KMg3AlSi3O ...

References

{{Reflist Epidote group Monoclinic minerals Minerals in space group 11

History

Composition

Structure

Geologic occurrence

See also

References