**2.2.5. Fluorcaphite**

Fluorcaphite (SrCaCa3(PO4)3F [1],[77],[78]): the name of this mineral is an acronym for its elemental composition, i.e. fluorine, calcium and phosphorus. Fluorcaphite is a common accessory mineral in albitite,14 which developed at the contact between quartzite and peralka‐ line nepheline syenites15 of the Lovozero complex, in northwestern Russia. The rock consists predominantly of albite, aegirine, sodic amphibole (arfvedsonite (NaNa2(Fe2+4Fe3+) Si8O22(OH)2) [79] – magnesio-arfvedsonite (NaNa2(Mg4Fe3+)Si8O22(OH)2) [80],[81] and narsar‐ sukite (Na2(Ti,Fe,Zr)Si4(O,F)11) [82].

Fluorcaphite forms euhedral prismatic crystals up to 0.3 mm in length. Most of the crystals are homogeneous, but a few contain resorbed core relatively depleted in Sr, Na and light rareearth elements (LREE). This pattern of zoning arose from two overprinting episodes of metasomatism16 [83],[84]. In terms of composition, both the core and the rim are intermediate members of a solid solution between fluorapatite and belovite-(Ce). The structure and the crystal habit of the mineral fluorcaphite is shown in **Fig. 24**.

**Fig. 24** The structure (view along *c*-axis) and the crystal habit of the mineral fluorcaphite.

Fluorcaphite is light or bright yellow hexagonal mineral which crystallizes in the space group P63 with the crystallographic parameters *a* = 9.485, *c* = 7.000 Å, *a*:*c* = 1:0.738, *V* = 545.39 Å3 and *Z* = 2. It has white streaks, vitreous luster and the hardness on the Mohs scale is 5. Calculat‐ ed and measured densities are 4.09 and 3.6 g·cm−3, respectively. Fluorcaphite does not show any cleavage, the mineral is brittle with the formation of subconchoidal fractures.

<sup>14</sup> Granular rock essential consisting of the mineral albite.

<sup>15</sup> Coarse-grained intrusive rock crystallized slowly under conditions similar to granite, but is deficient of quartz.

<sup>16</sup> The term was introduced by NEUMANN [83]. Metasomatism is a metamorphic process by which the chemical composi‐ tion of a rock or rock portion is altered in a pervasive manner and which involves the introduction and/or removal of chemical components as the results of the interaction of the rock with aqueous fluids (solutions). During the metasoma‐ tism, the rock remains in a solid state.
