Other Minerals from the Supergroup of Apatite

The supergroup of apatite is divided into five groups of minerals. Therefore, minerals from the group of apatite were described in the first chapter, the second chapter of this book continues with description of minerals from the other four groups, i.e. minerals from the group of britholite, belovite, ellestadite and hedyphane. The structure, properties and known localities of these minerals were described. Although carbonate-apatite species are discredited from the IMA list of minerals, the chapter ends with description of structure and properties of carbonate-hydroxylapatite, carbonate-fluorapatite, and carbonate-rich varieties of apatite, i.e. francolite, dahlite, kurskite and collophane. The introduced three basic types of carbonate-apatites, i.e. type A, B and AB) are then discussed in Chapter 10 in depth.

Distribution of described minerals from the supergroup of apatite (discredited species are also included) among individual groups (a) and distribution of kind of XO 4 tetrahedra (b), crystal system (c) and space group (d) among these species.
Other minerals from the supergroup of apatite include 65%, i.e. 28 described mineral species Fig. 1(a), which predominantly crystallize in hexagonal system (c) and in the space group P6 3 /M (d). The [PO 4 ] 3− unit is the most frequent ortho-oxyanion for the supergroup of apatite in general (b), but its content in individual groups varies strongly (Fig. 2).  Fig. 7 and Fig. 9), which is characteristic for the Pb 2+ ion in many compounds [6], [3], [7].
Fluorphosphohedyphane has the apatite structure with the ordering of Ca and Pb in two cation sites, as in hedyphane and phosphohedyphane. The Pb 2+ cation exhibits a stereoactive 6s 2 lone electron pair 6 [21] (Fig. 7). The Z anion site at (0, 0,½) is fully occupied by F forming six bonds of 2.867 Å to Pb atoms, in contrast to six Pb-Cl bonds of 3.068 Å in phosphohedyphane. For fluorphosphorhedyphane, phosphohedyphane and hedyphane in which Ca 2+ occupies the M(1) site and Pb 2+ occupies the M(2) site, the M(1) metaprism twist angles are notably smaller, 10.0°, 8.6° and 5.2°, respectively [8].
The mineral is brittle with subconchoidal fracture and no cleavage. Based on the empirical formula, the calculated density is 5.45 g·cm −3 . Fluorphosphohedyphane is hexagonal with the space group P6 3 /M and the cell parameters a = 9.6402, c = 7.0121 Å, a:c = 1:0.727, V = 564.4 Å 3 and Z = 2. The hardness of the mineral on the Mohs scale is 4.
The mineral is a phosphate analogue of hedyphane and possesses an apatite structure with the ordering of Ca and Pb in two nonequivalent large cation sites. The structure refinement indicates that the Ca(2) sites are completely occupied by Pb and the Ca(1) sites contain 92% Ca and 8% Pb. The tetrahedral site refines to 91% P and 9% As. The refinement indicates the 0,0,0 position to be fully occupied by Cl. The structure and the crystal habit of phoshohedyphane are shown in Fig. 9.
The structure of aiolosite shows two independent cationic sites M(1) and M (2). Due to close similarity in ionic radii of Na + and Bi 3+ , Bi exclusively prefers the M(2) site instead of M(1), which can be ascribed mainly to the Coulombic effect, in view of the higher charge of Bi 3+ compared to Na + , since the average M(2)-O distance (2.516 Å) is shorter than that of M(1)-O (2.617 Å). A similar effect also affects the distribution of Na + and Ca 2+ sites in cesanite (Section 2.1.7) [7].

Caracolite
Caracolite (Na 2 (Pb 2 Na)(SO 4 ) 3 Cl, sodium lead hydroxylchlorosulfate [1], [42], [43], [44]), is a vitreous colorless or grayish mineral from Beatriz mine, Caracoles, Chile, which was reported by WEBSKY in 1886. Known localities and the structure of the mineral caracolite are shown in Fig. 14. It occurs as crystalline incrustations with imperfect pseudohexagonal crystals up to 1 mm large. The crystals have the form of hexagonal pyramids with the base and the prism, but they are supposed to be pseudohexagonal. The mineral exhibits complex polysynthetic twinning with rather large extinction angles.  Caracolite is monoclinic mineral with the space group P2 1 /M and the cell parameters a = 19.62, b = 7.14, c = 9.81 Å and β = 120°, V = 1190.14 Å 3 , Z = 4. Calculated density is 4.50 g·cm −3 . The hardness of the mineral on the Mohs scale is 4½. The structure of caracolite is shown in Fig. 15.

Cesanite
Cesanite (Ca 2 Na 3 (SO 4 ) 3 OH [45], [46], [47]) is a colorless, medium to coarse-grained, soft mineral which occurs both as a solid vein (1 cm thick) and as cavity-filling of an explosive breccia in core samples of the Cesano-I geothermal well (Cesano area, Latium, Italy). Cesanite was recognized as new mineral by CAVARRETA et al [47]. The crystal structure determination confirms that cesanite has to be considered a member of the apatite-wilkeite-ellestadite series, where (PO 4 ) 3− is entirely substituted by (SO 4 ) 2− , the charge balance being made up by partial substitution of Na + for Ca 2+ and H 2 O for (OH − , Cl − , F − ).
The general formula of this series, proposed by HARADA et al [48] and modified by CAVARRE-TA et al [47], is as follows: Cesanite is a hexagonal mineral with the space group P6 and the cell parameters a = 9.463, c = 6.9088 Å, V = 535.79 Å 3 and Z = 1. Calculated density of the mineral is 2.75 g·cm −3 . The hardness of the mineral on the Mohs scale ranges from 2 to 3.
The structure of cesanite is shown in Fig. 16. Synthetic and natural cesanite show typical elements of the apatite structure, but the reduction of symmetry from the centrosymmetric space group P6 3 /M to the noncentrosymmetric space group P6 leads to a doubling of the number of crystallographically independent sites. Na and Ca cations are distributed over four independent sites. They are coordinated either by six O atoms and one hydroxyl ion or by water molecule (M(1), M(2)) or nine O atoms (M(3), M(4)) [46].

The group of belovite
The minerals from the group of belovite are cation ordered. Strontium substitutes for Ca in the M(2) site, and Na + REE substitute for Ca in the M(1) site. This results in lowering of symmetry from P6 3 /M (the space group of the apatite archetype structure) to P6 3 (fluorstrophite, fluorcaphite), P3 (belovites), or P3 (deloneite) [1].

Fig. 18
The structure of belovite-(Ce) (perspective view according to the c-axis; a) and the shape of belovite-(Ce) crystals (b).
Belovite-(Ce) is the cerium analogue of belovite-(La) (Section 2.2.2) and the strontium analogue of kuannersuite-(Ce) (Section 2.2.7). The ideal formula of belovite-(Ce) is Sr 6 (Na 2 REE 2 ) (PO 4 ) 6 O 24 (OH,F,Cl) 2 , and it is equivalent to apatite sensu stricto 10 with the following substitution of Ca(2) −6 Sr +6 and Ca(1) −4 Na +2 REE +2 . Strontium overcomes the REE in the competition for Ca(2) sites of apatite. The sites equivalent to Ca(1) of apatite must respond to the occupation by essentially equal amounts of Na and REE. Unlike single Ca(1) site in apatite sensu stricto, low symmetry in the space group P3 yields two Ca(1) subequivalents, one dominated by Na and the other one by REE [51].
Belovite-(Ce) is a brittle mineral with a honey-yellow or greenish color that crystallizes in trigonal system with the unit cell parameters a = 9.692 and c = 7.201Å, a:c = 1 : 0.743, V = 585.80 Å 3 and Z = 2. It has white streaks, (sub-)vitreous, resinous or greasy luster and a hardness on the Mohs scale of 5. Calculated and measured densities of the mineral are 4.23 and 4.19 g·cm −3 , respectively. It has imperfect prismatic and pinacoidal cleavage. 11

Deloneite
Deloneite ((Na 0.5 REE 0.25 Ca 0.25 )(Ca 0.75 REE 0.25 )Sr 1.5 (CaNa 0.25 REE 0.25 )(PO 4 ) 3 F 0.5 (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 mathematical crystallographer BORIS NIKOLAEVICH DELONE. The mineral usually occurs as anhedral to subhedral 2 crystals in the matrix. The locality and the structure of the mineral are shown in Fig. 22 and Fig. 23, respectively.   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 Å 3 and Z = 2. The mineral is brittle, with a vitreous luster, white streak, an average density of 3.93 g·cm −3 and a hardness on the Mohs scale that is equal to 5.

Fluorcaphite
Fluorcaphite (SrCaCa 3 (PO 4 ) 3 F [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 peralkaline nepheline syenites 15  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 metasomatism 16 [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. 14 Granular rock essential consisting of the mineral albite. 15 Coarse-grained intrusive rock crystallized slowly under conditions similar to granite, but is deficient of quartz.

The group of britholite
Britholites are typically phosphorus-bearing silicates with apatite structure and general formula: (REE,Ca) 5 [(Si,P)O 4 ] 3 Z, where REE is usually yttrium and Z = OH − , F − or Cl − . The minerals from the group of britholite usually contain significant impurities of thorium and sometimes also uranium. These minerals are widespread in alkaline rocks such as pegmatites and metasomites 19 related to syenite 15 and nepheline-syenite complexes [102]. The name of this group is derived from the Greek word brithos for weight in order to refer to the high density of the mineral. The following minerals are described below.
The structure and the crystallographic data of some of the minerals from the group of britholite were introduced in Fig. 29 and Table 1, respectively. The structural, thermodynamic and electronic properties of britholites were investigated by NJEMA et al [103]. 19 The series of metamorphic processes whereby chemical changes occur in minerals or rocks as the result of the introduction of material, often in hot aqueous solutions, from external sources.  Measured/calculated Table 1 The crystallographic data of minerals from the group of britholite
The specimen was named and described by CHR. WINTHER [104]  , which are apparently hexagonal prisms with pyramids, but it actually consists of biaxial orthorhombic individuals twined together as in aragonite. The Th-rich britholite-(Ce) was also known as fenghuangshite [107]. Britholite-(Ce) (first described as britholite) is the forefather of the   britholite group [108]. The structure of monoclinic britholite-(Ce) is shown in Fig. 32 and the crystallographic data are listed in Table 1.
The crystal structure of monoclinic dimorphs Fig. 33 of the mineral britholite-(Ce) (and also of britholite-(Y)described below) was solved in P2 1 space group by NOE et al [106].  britholite due to removal of symmetry elements 3 and M. The reduction in symmetry explains the common observation of biaxial optical characteristics of britholite samples [106].

Fluorbritholite-(Y)
The mineral fluorbritholite-(Y) ((Y,Ca) 5 (SiO 4 ) 3 F) [108]) was named as the fluorine-dominant analogue of britholite-(Y), where the Levinson-type suffix modifier, -(Y), indicates the dominance of yttrium among rare-earth elements. It forms irregular grains, hexagonal to tabular crystals and short-prismatic to thick-tabular crystals. The known localities and structures of the mineral fluorbritholite-(Y) are shown in Fig. 38 and Fig. 39, respectively.  . It has a pale brownish or white streak and its hardness on the Mohs scale is 5.

Fluorcalciobritholite
The mineral fluorcalciobritholite ((Ca,REE) 5 (SiO 4 ,PO 4 ) 3 F; [1], [102]) was found at Mount Kukisvumchorr, Khibiny alkaline complex, Kola Peninsula, Russia and differs from fluorbritholite and fluorapatite in the content of calcium (Ca > Σ REE) and phosphorus (Si > P), respectively. The main crystal form is a hexagonal prism. The mineral is transparent, with a pale pinkish to brown color and a white streak. The structure and the locality of fluorcalciobritholite is shown in Fig. 40 and Fig. 41, respectively.  , respectively. It has white streak and vitreous luster. The mineral is brittle and its hardness on the Mohs scale is equal to 5½.

The group of ellestadite
Ellestadites sensu lato are sulfato-silicates. For stoichiometric reasons, the incorporation of the sulfate anion (SO 4 ) 2− in the structure of apatite in the place of (PO 4 ) 3− or (AsO 4 ) 3− must be coupled with a concurrent substitution by silicate anions (SiO 4 ) 4− . This holds in all cases in which the M sites are occupied by divalent cations. Pure sulfates with an apatite structure may occur only by reducing overall positive charge associated with the M cations, as is the case in cesanite and caracolite from the group of hedyphane (Section 2.1) [1].
The structural formula of ellestadite and (with slight modification) of wilkeite can be expressed as follows [117]: This formula indicates that two-fifths of the Ca 2+ ions are located on threefold axes and can be replaced by carbon. Three-fifths of the Ca 2+ ions are tied to F − , Cl − and O − anions or OH − groups and cannot be replaced by carbon. All Ca 2+ ions are tied to O-ions, which are arranged in tetrahedral coordination with S-, Si-, P-or C-ions at the centers.

Fluorellestadite
The mineral fluorellestadite (formerly called ellestadite-(F) [85], [118], [119] Ca 5 (SiO 4 ) 1.5 (SO 4 ) 1.5 F [1], [120]) is a rare mineral found in nature in skarns or metamorphosed limestones 21 [121]. It was named according to American analytical chemist R.B. ELLESTAD and fluorine in the chemical composition. The mineral occurs as needles, as hexagonal prismatic, poorly terminated crystals up to 3 mm long, and as fine-grained aggregates. Thin needles are colorless, crystals are transparent and aggregates are translucent. Known localities of fluorellestadite are introduced in Fig. 45. The structure of mineral ellestadite is shown on Fig. 46. Fluorellestadite is colorless, blue or pale bluish green hexagonal mineral belonging to the space group P6 3 /M. The unit cell parameters are a = 9.485, c = 6.916 Å, Z = 2 and V = 538.84 Å 3 . Calculated density is 3.10 g⋅cm −3 . The hardness of the mineral on the Mohs scale is 4½.
The mineral is also known from burned coal dumps, where its formation is possible in the presence of carbonaceous and carbonate rocks such as the rests of pyrometamorphism 22 [9] of sedimentary rocks. The generalized formula of this mineral can be expressed as Ca 10 (SiO 4 ) 3−x (SO 4 ) 3−x (PO 4 ) 2x (OH,F,Cl) 2 , where the parameter x varies from 0 (ellestadite) to 3 (apatite).
Natural hydroxylellestadite 23 occurrences were reported from pegmatite veins, skarn and pyrometamorphic deposits and from mine dumps, but this mineral has never been reported from a cave. The mineral forms aggregates of xenomorphic crystals which have a maximum length of 0.5 mm and a maximum width of about 0.1 mm.

Fig. 47
Known localities for the mineral hydroxylellestadite. 23 Synthetic analogs are known as "technical products," such as burnt industrial waste and cement [122]. Hydroxylellestadite is associated with berlinite 24 (AlPO 4 [126]) , another high-temperature mineral. It is likely to have formed within highly phosphatized, silicate-rich, carbonatemudstone sediments heavily compacted and thermally transformed due to in situ bat guano combustion. Known localities, where the mineral hydroxylellestadite can be found, and its structure are shown in Fig. 47 and Fig. 48, respectively.
Hydroxylellestadite is a pink or purple-gray hexagonal mineral, which belongs to the space group P6 3 /M. The unit cell parameters are a = 9.491, c = 6.921 Å, Z = 2 and V = 539.91 Å 3 .
Calculated density is 3.11 g⋅cm −3 . The hardness of the mineral on the Mohs scale is in the range of 3½ to 4½. Hydroxylellestadite shows faded white-yellow fluorescence when irradiated with UV light, independently of the excitation frequency [122].

Chlorellestadite
The mineral chlorellestadite 25 [127], [128] was named in 1892 according to American analytical chemist R.B. ELLESTAD (Section 2.4.1) and the content of chlorine in its chemical composition in veinlets cutting contact with metamorphosed limestone. The structure of the mineral ellestadite is shown in Fig. 49.
The mineral occurs as a compact mass. The mineral chlorellestadite is associated with diopside, wollastonite, vesuvianite (Ca 10 Mg 2 Al 4 (SiO4) 5 (Si 2 O 7 ) 2 (OH) 4 [129]), monticellite (CaMgSiO 4 [130]) and calcite. 24 The mineral was named after Swedish pharmacologist N.J. BERLIN. The mineral is Al-P analogue of quartz. 25 The IMA status of the mineral was discredited in 2010. Chlorellestadite is a hexagonal mineral that crystallizes in the space group P6 3 /M with crystallographic parameters a = 9.53 and c = 6.91 Å, a:c = 1:0.725, V = 543,49 Å 3 and Z = 2. It has white streaks and a vitreous luster. The color of the mineral is pink, yellowish green, pale rose, orange, but it can also be colorless. The hardness on the Mohs scale is 4½. Calculated and measured densities of the mineral are 3.068 and 3.113 g⋅cm −3 , respectively.
Mattheddleite is a colorless or white hexagonal mineral belonging to the space group P6 3 /M.

Pieczkaite
The mineral pieczkaite (Mn 5 2+ (PO 4 ) 3 Cl [135], [136]) was found in the Southeastern shoreline of a small, unnamed island in Cross Lake, Manitoba, Canada (54°41′N, 97°49′W; Fig. 52) and classified as the member of the supergroup of apatite. It is isostructural with calcium fluorapatite (Section 1.5.1). The approximate composition of hydrothermally grown manganese chlorapatite is Mn 5 (PO 4 ) 3 Cl 0.9 (OH) 0.1 [136].   It is a hexagonal mineral that crystallizes in the space group P6 3 /M with the crystallographic parameters of unit cell a = 9.532 and c = 6.199 Å, a:c = 1:0.6501, V = 587.78 Å 3 and Z = 2. Calculated density of pieczkaite is 3.783 g·cm −3 . The hardness of the mineral on the Mohs scale varies in the range from 4 to 5. The structure of the mineral pieczkaite is shown in Fig. 53.
The coordination polyhedron around Mn(1) has the point-group symmetry 3 and is a trigonal prism in which the two triangles of oxygen atoms are slightly rotated relative to each other.
The coordination polyhedron around Mn (2) is a severely distorted octahedron. The phosphate group is more distorted than in any of the other apatites. The chlorine atom is located in the center of an equilateral triangle formed by three Mn (2) atoms [136].

Carbonate-apatites
As mentioned previously (Section 1.1) the name of both most typical examples, i.e. carbonate-hydroxylapatite (Ca 5 (PO 4 ,CO 3 ) 3 OH) and carbonate-fluorapatite (Ca 5 (PO 4 ,CO 3 ) 3 F), was discredited from the IMA list of minerals [1]. The structure and the crystal shape of carbonate-apatite and carbonate-fluorapatite are shown in Fig. 54. The carbonate-apatites, the properties of which are listed in Table 7 (Chapter 1), are intensively studied as the mineral constituents of bones and teeth as described in Section 10.9.
This complex carbonate-substituted apatite is found only in marine environments, and, to a much smaller extent, in weathered deposits, for instance above carbonatites [138]. The mineral was named according to its occurrence at Wheal Franco, Whitchurch, Tavistock District, Devon, England.
3. Kurskite (Ca 10 P 4.8 C 1.2 O 22.8 F 2 (OH) 1.2 ) [137], [141], [142] forms nodular or platform-type phosphorites, widespread within Russia. It is a carbonate-rich mineral that can be found in two varieties: • Radiating (previously incorrectly termed as staffelite) • Optically amorphous The mineral is usually gray or brown due to the content of organic, humic or ferruginous impurities. Sometimes, it is white or black colored. Pure kurskite has a specific gravity of 3 g·cm −3 .
According to the accommodation of carbonate ion in the apatite structure, three basic types of apatites (Fig. 55) can be recognized [144]: i.

Author details
Petr Ptáček Brno University of Technology, Czech Republic