**2.2.4. Deloneite**

Belovite-(La) can be found in natrolite veinlets12

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

cline and natrolite.

Carlgieseckeite-(Nd)13

**2.2.3. Carlgieseckeite-(Nd)**

massif [70]), lamprophyllite, murmanite, aegirine, pectolite (NaCa2Si3O8(OH) [71]), micro‐

gist and polar explorer GIESECKE with respect to the content of Nd that is higherthan the content of other REE. The mineral was found in Kuannersuit (formerly Kvanefjeld) Plateau, north‐ ern section of the Ilímaussaq alkaline complex, South Greenland, Denmark. It is associated with albite (NaAlSi3O8 [74]), analcime (NaAlSi2O6·H2O [75]) and fluorapatite in the cavities of albite vein cross-cutting augite syenite. Carlgieseckeite-(Nd) forms hexagonal tabular crystals up to 0.25 × 1 × 1.3 mm, and their parallel intergrowth up to 0.7 × 1.3 mm is found epitactical‐ ly overgrown on prismatic crystals of fluorapatite. A phase with idealized formula

The structure of the mineral (**Fig. 21**) is representative of the structure type of belovite *sensu stricto*. In this structure, large M cations occupy three sites with different coordination numbers: 9-fold polyhedra M(1) (average distance <M(1)–O> is 2.522 Å), 6-fold polyhedral M(1)′ (reduced 9-fold polyhedra, <M(1)′–O> with average interatomic distance 2.445 Å) and

is the isostructural Ca- and Nd-dominant analogue of belovite-(Ce) and belovite-(La). The mineral carlgieseckeite-(Nd) is colorless, transparent and shows a distinct color-change effect, from almost colorless with a greenish hue in daylight to pink in yellow electric light. The luster is vitreous. The Mohs hardness is about 5. The mineral is brittle with no observed cleavage [72].

<sup>13</sup> The holotype material is deposited in the Fersman Mineralogical Museum of Russian Academy of Sciences, Moscow

Na1.5Nd1.5Ca2(PO4)3F epitactically overgrows some crystals of carlgieseckeite-(Nd).

7-fold polyhedra M(2) (<M(2)–O,F > 2.486 or 2.560 Å in the case of F1) [72].

**Fig. 21** The structure of carlgieseckeite -(Nd) (perspective view according to the *c*-axis).

Mineral carlgieseckeite-(Nd) is trigonal, from the space group P3

parameters *a* = 9.4553, *c* = 6.9825 Å, *a*:*c* = 1:0.738, *V* = 540.62 Å3

12 Sheetlike body of minerals which crystallize within the rock.

[72].

(NaNdCa3(PO4)3F [31],[72],[73]) was named according to the mineralo‐

in pegmatites in a differentiated alkalic

¯ with crystallographic cell

and *Z* = 2. Carlgieseckeite-(Nd)

Deloneite ((Na0.5REE0.25Ca0.25)(Ca0.75REE0.25)Sr1.5(CaNa0.25REE0.25)(PO4)3F0.5(OH)0.5 [1],[76]): the name of the mineral was changed from deloneite-(Ce) to deloneite. The mineral was named by KHOMYAKOV, LISITIN, KULIKOVA and RASTSVETAEVA in 1996 according to Russian mathemati‐ cal crystallographer BORIS NIKOLAEVICH DELONE. The mineral usually occurs as anhedral to subhedral2 crystals in the matrix. The locality and the structure of the mineral are shown in **Fig. 22** and **Fig. 23**, respectively.

**Fig. 22** The locality of deloneite.

**Fig. 23** The structure of the mineral deloneite (perspective view according to the *c*-axis).

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‐ ness on the Mohs scale that is equal to 5.
