**2.2.1. Belovite-(Ce)**

recognized as new mineral by CAVARRETA et al [47]. The crystal structure determination confirms that cesanite has to be considered a member of the apatite-wilkeite-ellestadite series,

> , Cl<sup>−</sup> , F<sup>−</sup> ).

The general formula of this series, proposed by HARADA et al [48] and modified by CAVARRE‐

Ca5−*w*Na*w*(Si *<sup>y</sup>*, S*z*, P3−*y*−*<sup>z</sup>*)O12(F, Cl, OH)*<sup>x</sup> n*H2O;

6.9088 Å, *V* = 535.79 Å3 and *Z* = 1. Calculated density of the mineral is 2.75 g·cm−3. The hardness

The structure of cesanite is shown in **Fig. 16**. Synthetic and natural cesanite show typical elements of the apatite structure, but the reduction of symmetry from the centrosymmetric

of crystallographically independent sites. Na and Ca cations are distributed over four independent sites. They are coordinated either by six O atoms and one hydroxyl ion or by

**Fig. 16** The structure of cesanite (perspective view according to the *c*-axis; a), crystal habit (b) and the coordination

polyhedra for M(1) (1), M(2) (2), M(3) (3) and M(4) (4) in synthetic analogue of the mineral cesanite (c) [47].

2−, the charge balance being made up by partial

¯ and the cell parameters *a* = 9.463, *c* =

¯ leads to a doubling ofthe number

3− is entirely substituted by (SO4)

Cesanite is a hexagonal mineral with the space group P6

space group P63/M to the noncentrosymmetric space group P6

water molecule (M(1), M(2)) or nine O atoms (M(3), M(4)) [46].

of the mineral on the Mohs scale ranges from 2 to 3.

for Ca2+ and H2O for (OH<sup>−</sup>

72 Apatites and their Synthetic Analogues - Synthesis, Structure, Properties and Applications

where (PO4)

substitution of Na+

TA et al [47], is as follows:

where *w* = 1 – *x* – *y* + *z* and *n* ≤ 1 – *x*.

Belovite-(Ce) (NaCeSr3(PO4)3F [49],[50],[51]), is a mineral from alkaline pegmatite in differen‐ tiated alkalic massifs which was named in 1954 by L.S. Borodin and M.E. Kazakova accord‐ ing to Russian mineralogist and crystallographer N.V. BELOV. The mineral is found in Russia, on Mts. Punkaruaiv, Lepkhe-Nelm, Sengischorr, Karnasurt, Kedykvyrpakhk and Alluaiv, Lovozero massif; and on Mts. Kukisvumchorr and Koashva, Khibiny massif, Kola Peninsula. The localities of belovite-(Ce) are shown in **Fig. 17**.

**Fig. 17** The localities of the mineral belovite-(Ce).

The mineral belovite-(Ce) is usually associated with ussingite (Na2AlSi3O8(OH) [52]), natro‐ lite (Na2(Si3Al2)O10·2H2O [53]), chkalovite (Na2BeSi2O6 [54]), epistolite (Na4TiNb2 (Si2O7)2O2(OH)2·4H2O [55]), tugtupite (Na4BeAlSi4O12Cl [56]), manganneptunite (Na2KLi(Mn2+,Fe2+)2Ti2[Si8O24] and manganoneptunite [57] (the mineral is isostructural with neptunite [58],[59]), murmanite (Na2Ti2(Si2O7)O2·2H2O [60]), gaidonnayite (Na2ZrSi3O9·2H2O [61]), nordite-(La) (Na3SrLaZnSi6O17), lamprophyllite (Na3(Sr,Na)Ti3(Si2O7)2O2(OH)2 [62]), fluorcaphite, lomonosovite, deloneite-(Ce), sitinakite (KNa2Ti4Si2O13(OH)·4H2O [63]), aegir‐ ine (NaFe3+Si2O6 [64]), sodalite (Na4Si3Al3O12Cl [65]), microcline9 (KAlSi3O8 [66],[67]) and

<sup>9</sup> Originally, the mineral was named as mikroklin [66],[67]: triclinic mineral, space group *C*1 ¯ with the unit cell parameters: *a* = 8.5784 Å, *b* = 12.9600 Å, *c* = 7.2112 Å, *α* = 90.30°, *β* =116.03°, and *γ* = 89.125°.

(NaAlSiO4 [68]). The morphology of belovite-(Ce) crystals and its structure are shown in **Fig. 18**.

**Fig. 18** The structure of belovite-(Ce) (perspective view according to the *c*-axis; a) and the shape of belovite-(Ce) crys‐ tals (b).

Belovite-(Ce) is the cerium analogue of belovite-(La) (**Section 2.2.2**) and the strontium analogue of kuannersuite-(Ce) (**Section 2.2.7**). The ideal formula of belovite-(Ce) is Sr6(Na2REE2) (PO4)6O24(OH,F,Cl)2, and it is equivalent to apatite *sensu stricto*<sup>10</sup> with the following substitu‐ tion of Ca(2)−6Sr+6 and Ca(1)−4Na+2REE+2. Strontium overcomes the REE in the competition for Ca(2) sites of apatite. The sites equivalent to Ca(1) of apatite must respond to the occupation by essentially equal amounts of Na and REE. Unlike single Ca(1) site in apatite *sensu stricto*, low symmetry in the space group P3 ¯ yields two Ca(1) subequivalents, one dominated by Na and the other one by REE [51].

Belovite-(Ce) is a brittle mineral with a honey-yellow or greenish color that crystallizes in trigonal system with the unit cell parameters *a* = 9.692 and *c* = 7.201Å, *a*:*c* = 1 : 0.743, *V* = 585.80 Å3 and *Z* = 2. It has white streaks, (sub-)vitreous, resinous or greasy luster and a hardness on the Mohs scale of 5. Calculated and measured densities of the mineral are 4.23 and 4.19 g·cm −3, respectively. It has imperfect prismatic and pinacoidal cleavage.11
