**1.6.6. Alforsite**

pegmatite and Mt. Karnasurt, Lovozero alkaline complex, Kola Peninsula, Russia (**Fig. 29**),

was first reported as "strontium-apatite."

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

**Fig. 29.** Known localities for the mineral stronadelphite.

in **Fig. 30**.

Stronadelphite (Sr5(PO4)3F, strontium fluorophosphates, strontium apatite,49

**Fig. 30.** Structure (view according to the *c*-axis) and crystal habit of stronadelphite mineral.

consult with **Table 3**). The name fluorostrophite (**Section 2.2.6**) was suggested by PASSERO et al [45].

<sup>49</sup> Strontium apatite was also used as the old name for the mineral named apatite-(SrOH). The original name strontium– apatite was given before the structural study of the mineral and incorrectly reflects its relationship with apatite (please

SFAP [45],[179]) is a hexagonal mineral that crystallizes in the space group P63/M and has the cell parameters *a* = 9.845 and *c* = 7.383 Å, *a*:*c* = 1:0.75, *V* = 619.7 Å3 and *Z* = 2. The brittle mineral is transparent and colorless with a pale greenish tint. There are no cleavages, and the hard‐ ness of mineral on the Mohs scale is 5 (apatite). Calculated and measured densities of the mineral are 3.98 and 3.92 g·cm−3, respectively. The structure of mineral stronadelphite is shown

apatite–(SrF),

Alforsite (Ba5(PO4)3Cl, barium analogue of chlorapatite, barium chlorapatite, pentabarium tris[arsenate(V)] chloride [53],[54],[180]) is a colorless hexagonal mineral from the group of apatite named according to the geologist J.T. ALFORS. The mineral occurs in the localities introduced in **Fig. 31**.

**Fig. 31.** Known localities for the mineral alforsite.

**Fig. 32.** The structure of mineral alforsite (perspective view along the *c*-axis).

Alforsite occurs as isolated small subhedral grains, generally less than 0.05 mm in diameter but rarely up to 0.2 mm. These colorless grains resemble typical fluorapatite, exhibiting low birefringence and high relief. This makes it difficult to distinguish alforsite from fluorapatite and from many of the associated high-relief barium minerals except by using the electron microprobe. Mineral is uniaxial and negative, with extremely low birefringence [53].

The structure of mineral alforsite is shown in **Fig. 32**. The space group of alforsite is P63/M with the crystallographic parameters *a* = 10.25 Å, *c* = 7.64 Å, *a*:*c* = 1:0.745, *V* = 700.77 Å3 and Z = 2. The mineral hardness on the Mohs scale is equal to 5. Calculated and measured density of mineral are 4.81 and 4.77 g·cm−3, respectively [53],[54],[180].
