**1.6.5. Stronadelphite**

**Fig. 26.** The structure (perspective view along the *c*-axis) and the crystal habit of johnbaumite (a) and johnbaumite–M

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

The space group of johnbaumite is P63/M or P63 with *a* = 9.70 Å and *c* = 6.93 Å, *a*:*c* = 1:0.714, *V* = 564.96 Å3 and *Z* = 2. Johnbaumite occurs as massive anhedral grayish-white granular material with individual grains of approximately 8 mm or less in diameter and is white to colorless with vitreous luster. Johnbaumite is colorless in thin section and has white streaks. The Mohs hardness is approximately 4½. The luster is vitreous on cleavage surfaces and slightly adamantine to greasy on fracture surfaces. The cleavage is distinct, parallel to {100}. Measured and calculated density of mineral is 3.68 and 3.73 g·cm−3, respectively. Johnbaumite is fluorescent in short-wave UV radiation with a medium pinkish orange response color [165].

The monoclinic variant of mineral, which was previously named strontiumarsenapatit and fermorite (3[(Ca,Sr)3(P,As)2O8]·Ca(OH,F)2 [74],[167], is now named johnbaumite–M and is not considered a distinct species [45]. The mineral crystallizes in the space group P21/M with crystallographic parameters *a* = 9.594 Å, *b* = 6.975 Å and *c* = 9.579 Å; *α* = *γ* = 90° and *β* = 119.97°;

Pyromorphite (lead chlorophosphate, Pb5(PO4)3Cl [52],[168],[169],[170],[171],[172],[188], **Fig. 27**) was named by F.L. HAUSMANN in 1813. The name was derived from Greek words for "fire" and "form" to describe the recrystallization of a mineral from the melt. The structure and the example of shape of pyromorphite are shown in **Fig. 28**. Since the structures of vanadinite and pyromorphite are similar except for the tetrahedrally coordinated cations, it is

(b).

*V* = 556.341 Å3

**1.6.4. Pyromorphite**

described in **Section 1.6.8**.

; and *Z* = 2.

The mineral is named after the chemical element strontium and αδελϕóσ, Greek word for "brother," as the full strontium analogue of fluorapatite, the most widespread member of the apatite supergroup. The mineral chemically close to stronadelphite, found in peralkaline pegmatite and Mt. Karnasurt, Lovozero alkaline complex, Kola Peninsula, Russia (**Fig. 29**), was first reported as "strontium-apatite."

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

Stronadelphite (Sr5(PO4)3F, strontium fluorophosphates, strontium apatite,49 apatite–(SrF), 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 in **Fig. 30**.

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

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