**2.2.2. Belovite-(La)**

Belovite-(La) (NaLaSr3(PO4)3F [1],[69]) was named according to N.V. BELOV (**Section 2.2.1**) with respect to higher content of La than Ce, i.e. the mineral is the lanthanum analogue of belo‐ vite-(Ce) described above and NaSr3La analogue of fluorapatite (**Section 1.5.1**). It occurs as prismatic crystals, up to 3 cm large, and it may also be granular. The structure and the crystal habit of the mineral belovite-(La) are shown in **Fig. 19**.

<sup>10</sup> Latin phrase (abbreviated as s.s.) used, which means "in exact sense."

<sup>11</sup> Cleavage that is parallel to the orientation {0001}, i.e. to the base of crystal.

**Fig. 19** The structure (shown along the *c*-axis) and the crystal habit of the mineral belovite-(La).

The mineral belovite-(La) crystallizes as trigonal in the space group P3 ¯with the cell parame‐ ters *a* = 9.647 and *c* = 7.17 Å, *a*:*c* = 1:0.743, *V* = 577.88 Å3 and *Z* = 2. Belovite-(La) is a very brittle mineral with yellow or greenish-yellow color and vitreous luster that does not show appa‐ rent cleavage. It has measured and calculated densities of 4.19 and 4.05 g⋅cm−3, respectively. It has white streaks and the hardness of the mineral on the Mohs scale is equal to 5.

**Fig. 20** The locality of belovite-(La).

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

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

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

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)

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*,

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

 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

Belovite-(La) (NaLaSr3(PO4)3F [1],[69]) was named according to N.V. BELOV (**Section 2.2.1**) with respect to higher content of La than Ce, i.e. the mineral is the lanthanum analogue of belo‐ vite-(Ce) described above and NaSr3La analogue of fluorapatite (**Section 1.5.1**). It occurs as prismatic crystals, up to 3 cm large, and it may also be granular. The structure and the crystal

with the following substitu‐

¯ yields two Ca(1) subequivalents, one dominated by Na

(PO4)6O24(OH,F,Cl)2, and it is equivalent to apatite *sensu stricto*<sup>10</sup>

−3, respectively. It has imperfect prismatic and pinacoidal cleavage.11

habit of the mineral belovite-(La) are shown in **Fig. 19**.

10 Latin phrase (abbreviated as s.s.) used, which means "in exact sense." 11 Cleavage that is parallel to the orientation {0001}, i.e. to the base of crystal.

low symmetry in the space group P3

and the other one by REE [51].

**2.2.2. Belovite-(La)**

**18**.

tals (b).

Å3

Belovite-(La) can be found in natrolite veinlets12 in pegmatites in a differentiated alkalic massif [70]), lamprophyllite, murmanite, aegirine, pectolite (NaCa2Si3O8(OH) [71]), micro‐ cline and natrolite.
