**2.2.6. Fluorstrophite**

Deloneite is a bright yellow mineral which crystallizes in trigonal systems with the unit cell crystallographic parameters *a* = 9.51, *c* = 7.01 Å, *a*:*c* = 1:0737, *V* = 549.05 Å3 and *Z* = 2. The mineral is brittle, with a vitreous luster, white streak, an average density of 3.93 g·cm−3 and a hard‐

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

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

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‐

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

members of a solid solution between fluorapatite and belovite-(Ce). The structure and the

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

*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.

15 Coarse-grained intrusive rock crystallized slowly under conditions similar to granite, but is deficient of quartz. 16 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‐

which developed at the contact between quartzite and peralka‐

and

of the Lovozero complex, in northwestern Russia. The rock consists

[83],[84]. In terms of composition, both the core and the rim are intermediate

ness on the Mohs scale that is equal to 5.

**2.2.5. Fluorcaphite**

accessory mineral in albitite,14

sukite (Na2(Ti,Fe,Zr)Si4(O,F)11) [82].

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.

14 Granular rock essential consisting of the mineral albite.

tism, the rock remains in a solid state.

line nepheline syenites15

metasomatism16

Fluorstrophite (SrCaSr3(PO4)3F [1],[85],[86]) formerly "strontium-apatite" [87] and later changed to apatite-(SrOH) [1]. It possesses massive, coarse granular to compact morphology. The crystal forms include short to long hexagonal prisms, they can also be thick and tabular. Similar to fluorcaphite, the name of the mineral reflects its chemical composition (fluorine, strontium and phosphorus). The localities of the mineral fluorstrophite are shown in **Fig. 25**.


**Fig. 25** Localities for the mineral fluorstrophite.

**Fig. 26** The structure and the crystal habit of the mineral fluorstrophite.

The structure and the crystal habit of the mineral fluorstrophite are shown in **Fig. 26**. It is a green, yellow-green or colorless mineral with vitreous-greasy luster that crystallizes in hexagonal system with the space group P63/M or P63. The crystallographic parameters of the unit cell are *a* = 9.565 and *c* = 7.115 Å, the ration *a*:*c* = 1:0.744, *V* = 563.74 Å3 and *Z* = 2. The hardness of the mineral on the Mohs scale is 5. Calculated and measured densities are 3.74 and 3.84 g·cm−3, respectively. It has imperfect cleavage to {1010}.
