Symmetry Trends of Monoelement Minerals

GEOLOGICA BALCANICA, 40. 1–3, Sofia, Dec. 2011, p. 85–95.

Symmetry trends of monoelement minerals

Alexander Vlahov

Geological Institute, Bulgarian Academy of Sciences, 1113, Sofia, Bulgaria; E-mail: [email protected] (Accepted in revised form: November 2011)

Abstract. The number of the symmetry of each crystallographic class (NSCC) includes the sum of the orders of symmetry axes plus the number of symmetry planes plus one for a center of symmetry, if present. In 94.44% of cases, with increasing of NSCC values, the number of monoelement minerals crystallizing in the respective 3 3 symmetry classes also increases. The density values Dc (gm/Å ) and Dcalc (g/cm ) of the monoelement minerals decrease with the increase of the atomic weight of chemical elements with consecutive or close atomic numbers in the periodic table. The NSCC values show a tendency to decrease with decreasing temperature 3 and pressure of formation of monoelement minerals. At certain NSCC values, the highest the Dc (gm/Å ) and 3 Dcalc (g/cm ) of monoelement minerals, the less probable becomes the possibility their polymorphic forms to be 3 3 established. Polymorphic modifications denser than α-Fe (having Dc = 4.7049 gm/Å and Dcalc = 7.81 g/cm ) have not yet been established. The monoelement polymorphic modifications of As and S, crystallizing in the low symmetry crystal systems, are exceptions to Groth’s law. Most (91.67%) of the monoelement minerals crystallize in the holohedral classes. 2932 of all known 4106 mineral species (71.41%) also crystallize in the holohedral classes of different systems. The data presented suggest that the mineral species in general prefer holohedral classes, having also the highest NSCC values for the respective system. Therefore, the quantitative integral characteristic NSCC is informative in studies of all kinds of mineral assemblages grouped on the basis of different characteristics.

Vlahov, A. 2011. Symmetry trends of monoelement minerals. Geologica Balcanica, 40(1–3), 85–95. Key words: monoelement minerals, symmetry, Groth’s law, numerical characteristics, genesis.

Introduction At the beginning of the 20th century Paul von Groth established that the more complex the chemistry of The monoelement minerals often include negligible non organic compounds, the lower their symmetry is amounts of other elements that are not referred in their (Kostov, 1978). The explanation of this statement is that crystal-chemical formulae, and do not change signifi- the number of the most symmetric sites in each space cantly their lattice parameters, neither their properties. group is limited. In structures with simple composition Some of the native elements appear in two or more all atoms occupy high-symmetry sites. That is why the polymorphic modifications. They crystallize mainly minerals with simple chemical composition have high in the cubic, hexagonal, tetragonal and trigonal crys- symmetry. When many types of atoms are available, tal systems. The monoclinic and orthorhombic modi- the high-symmetry sites are insufficient and the symme- fications of native arsenic and sulfur are exceptions try of the structure decreases (Kostov, 1978; Kirov and to Groth’s law. The comparison of some quantitative Stanimirova, 2010). characteristics of the monoelement minerals consid- From depth towards the Earth’s surface there is a con- ering also the conditions of their formation allows: tinuous decrease of the total symmetry of mineral matter, as 1) to identify quantitative criteria, controlling the for- the number of the cubic minerals decreases at the expense mation of polymorphic modifications of native ele- of gradual increase in quantity of orthorhombic, monoclin- ments; 2) to indicate quantitative criteria of the excep- ic and triclinic minerals (Yushkin et al., 1987). The aver- tions to Groth’s law amongst the minerals with simplest age symmetry of the rare mineral species is considerably chemical composition; 3) to combine the new data with lower than the symmetry of the widely distributed ones. already known facts and, thus, to formulate more gen- This pattern becomes better expressed with increasing of eral natural patterns. the number of known minerals (Urusov, 2007).

85 Methodology Only six of the studied minerals (16.67%) are solid solutions and are built by two to four elements. These are

36 monoelement minerals formed by 27 native ele- native arsenic (pararsenolamprite – As0.94Sb0.05), native ments have been investigated here. Arranged in order ruthenium (Ru0.6Ir0.3Os0.1), native osmium (Os0.75Ir0.25), of increase of their atomic numbers in the periodic native palladium (Pd0.8Pt0.1Fe0.05), native rhodium table these elements are: C, Al, Si, S, Cr, Fe, Ni, Cu, (Rh0.75Pt0.25) and native iridium (Ir0.5Pt0.1Os0.3Ru0.1). They Zn, As, Se, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, Os, Ir, are included in the present study since they satisfy the Pt, Au, Hg, Pb, Bi. These elements have strongly vari- following requirements: 1) they are approved by IMA as able average contents in the Earth’s crust (Rudnik and mineral species (the only exceptions allowed are some Gao, 2003; Brownlow, 1984; Kostov, 1993). Most of polymorphs of iron considered as geothermometers); the studied monoelement minerals satisfy the mineral 2) the native element they refer to or are named after is definition and are approved as mineral species by IMA present in largest atomic quantities; 3) all elements present (Nickel, 1995). Four of them appear in nature in several in the crystal-chemical formulae are related and situated polymorphic modifications. The polymorphs of carbon close to each other in the periodic table; 4) presence of (diamond, lonsdaleite, chaoite and graphite), sulfur elements with no close chemical relationship has been (α-S and rosickyite), iron (α-Fe, β-Fe, γ-Fe, δ-Fe) and allowed only in case they are in negligible amounts. arsenic (trigonal arsenic, arsenolamprite, pararsenolam- This study also considers parameters such as the prite) have also been considered. atomic numbers of native elements (Table 1), calculated

Table 1 Numbers of chemical elements in the periodical system, atomic weights, native minerals and their calculated densities

Number in the Atomic weight Native Element D calc (g/cm3) Periodical System (gm) elements C 6 12.0107 Diamond 3.52 C 6 12.0107 Lonsdaleite 3.52 C 6 12.0107 Chaoite 3.43 C 6 12.0107 Graphite-2H 2.26 Al 13 26.981538 Aluminum 2.72 Si 14 28.0855 Silicon 2.33 S 16 32.065 α – Sulfur 2.08 S 16 32.065 γ – Sulfur 2.00 Cr 24 51.9961 Chromium 7.20 Fe 26 55.845 α - Iron 7.81 Fe 26 55.845 β – Iron 7,60 Fe 26 55.845 γ – Iron 7,63 Fe 26 55.845 δ – Iron 7.33 Ni 28 58.6934 Nickel 8.91 Cu 29 63.546 Copper 8.93 Zn 30 65.409 Zinc 7.19

As 33 74.9216 Pararsenolamprite – As 0,94Sb 0,05 6.47 As 33 74.9216 Arsenic 5.74 As 33 74.9216 Arsenolamprite 5.62 Se 34 78.96 Selenium 4.81 Ru 44 101.07 Ruthenium 16.65 Rh 45 102.9055 Rhodium 14.59 Pd 46 106.42 Palladium 12.19 Ag 47 107.8682 Native Silver 10.50 Cd 48 112.411 Cadmium 8.65 In 49 114.818 Indium 7.29 Sn 50 118.710 Tin 7.29 Sb 51 121.760 Antimony 6.74 Te 52 127.60 Tellurium 6.27

Os 76 190.23 Osmium (Os0,75Ir0,25) 23.01

Ir 77 192.217 Iridium (Pt0,1Ir0,5Os0,3Ru0,1) 21.45 Pt 78 195.078 Platinum 21.46 Au 79 196.96655 Native Gold 19.28 Hg 80 200.59 Mercury 14.49 Pb 82 207.20 Lead 11.34 Bi 83 208.98038 Bismuth 9.87

86 3 density of minerals – Dcalc (g/cm ) and unit-cell density egories has also been studied. A quantitative correlation 3 – Dc (gm/Å ). The latter two parameters depend on the between the number of monoelement minerals crystalliz- conditions of mineral formation, their chemical compo- ing in different crystallographic classes and the values of sition and structure and also combine other numerical NSCC (the number of symmetry of each crystallographic characteristics of lower rank: unit-cell dimensions (Å) class) has been identified. NSCC was defined as the sum and angles (αо, βо, γо); Z – number of the atoms or ions in of orders of the symmetry axes plus the number of sym- 3 the unit cell; Vc (Å ) – unit-cell volume and; Mc – unit- metry planes plus one for a center of symmetry, if present cell weight (Table 2). (Vlahov, 2010). The distribution of the 36 monoelement minerals By analyzing the relationships between these integral within the different symmetry systems and symmetry cat- numerical characteristics and conditions of formation of

Table 2 IMA-status, symmetry, characteristics and genesis of native elements

Native elements – symmetry and characteristics Genesis Pt: Valid Species (Pre-IMA) 1748; Pt and chromite crystallize over 1300–1500 °C in ul- m3m; NSC = 46; Z = 4; Vc = 60.379 Å3; Mc = 780.312 gm; trabasic and basic magmas. Below this temperature Pt 3 3 Dc = 12.9236 gm/Å ; Dcalc=21.46 g/cm forms with sulfides and NiAs2.

Ir (Pt0,1Ir0,5Os0,3Ru0,1): Valid Species (Pre-IMA) 1804; m3m; NSC = 46; Z = 4; Vc = 56.596 Å3; Mc = 731.168 gm; As particles in Pt-Fe alloys. Dc = 12.9191 gm/Å3; Dcalc = 21.45 g/cm3 Au: Valid Species (Pre-IMA) Prehistoric; In hypothermal deposits - native gold. In mesothermal m3m; NSC = 46; Z = 4; Vc = 67.847 Å3 Mc = 787.866 gm; – native and dispersed gold in sulfides. In epithermal – Dc = 11.6124 gm/Å3; Dcalc = 19.28 g/cm3 with sulfides, quartz. Rh (Rh Pt ): Approved IMA 1974; 0,75 0,25 Grains are discovered in the heavyweight fraction of m3m; NSC = 46; Z = 4; Vc = 57.334 Å3; Mc = 503.796 gm; ultrabasic intrusion. Dc = 8.7870 gm/Å3; Dcalc = 14.59 g/cm3 Pd (Pd Pt Fe ): Valid Species (Pre-IMA) 1803; m3m; 0,8 0,1 0,05 Palladium forms by oxidation of primary Pd-bearing NSC = 46; Z = 4; Vc = 58.52 Å3; Mc = 429.744 gm; sulfides in Pt deposits. Dc = 7.3435 gm/Å3; Dcalc = 12.19 g/cm3 Pb: Valid Species (Pre-IMA) Prehistoric; Rare hydrothermal mineral. It can form by autigenic m3m; NSC = 46; Z = 4; Vc = 121.324 Å3; Mc = 828.800 gm; processes. Dc = 6.8313 gm/Å3; Dcalc = 11.34 g/cm3 Ag: Valid Species (Pre-IMA) Prehistoric; Silver forms in sulfide veins by hydrothermal processes m3m; NSC = 46; Z = 4; Vc = 68.227 Å3; Mc = 431.473 gm; and by reduction weathering of silver minerals. Dc = 6.3241 gm/Å3; Dcalc = 10.50 g/cm3 Cu: Valid Species (Pre-IMA) Prehistoric; Copper is found in upper parts of sulfide veins in some m3m; NSC = 46; Z = 4; Vc = 47.242Å3; Mc = 254.184 gm; volcanic rocks. It forms in the supergenic zone of Dc = 5.3805 gm/Å3; Dcalc = 8.93 g/cm3 sulfide copper deposits. Ni: Approved IMA 1967; Nickel forms from low-temperature hydrothermal m3m; NSC = 46; Z = 4; Vc = 43.756 Å3; Mc = 234.774 gm; solutions in serpentinized ultrabasic rocks. Dc = 5.3655 gm/Å3; Dcalc = 8.91 g/cm3 α - Fe: Valid Species (Pre-IMA) Prehistoric; m3m; NSC = 46; Iron occurs in meteorites and rarely in basaltic rocks. Z = 2; Vc = 23.739 Å3; Mc = 111.69 gm; Stable modification below 770 °С. Dc = 4.7049 gm/Å3; Dcalc = 7.81 g/cm3 β - Fe: m3m; NSC = 46; Z = 2; Vc = 24.389 Å3; Mc = 111.69 gm; Stable modification between 770 and 920 °С. Dc = 4.5795 gm/Å3; Dcalc = 7.60 g/cm3 γ - Fe: m3m; NSC = 46; Z = 4; Vc = 48.587 Å3; Mc = 223.38 gm; Stable modification between 920 and 1400 °С. Dc = 4.5975 gm/Å3; Dcalc = 7.63 g/cm3 δ - Fe: m3m; NSC = 46; Z = 2; Vc = 25.283 Å3; Mc = 111.69 gm; Stable modification above 1400 °С. Dc = 4.4176 gm/Å3; Dcalc = 7.33 g/cm3 Cr: Approved IMA 1981; m3m; Z = 2; Vc = 23.985 Å3; NSC = Chromium is found in the contact zone between marbles 46; Mc = 103.992 gm; Dc = 4.3357 gm/Å3; Dcalc = 7.20 g/cm3 and ultrabasic rocks. С: (Diamond): Valid Species (Pre-IMA) Prehistoric; m3m; In ultrabasic kimberlite pipes from mantle depths. NSC = 46; Z = 8; Vc = 45.377 Å3; Mc = 96.0856 gm; Micro-diamonds form in high-pressure metamorphic Dc =2.1175 gm/Å3; Dcalc = 3.52 g/cm3 rocks. Al: Approved IMA 1978; m3m; NSC = 46; Z = 4; Vc = 65.939 Å3; Minor phase in low oxygen fugacity environments. Mc = 107.926 gm; Dc=1.6367 gm/Å3; Dcalc = 2.72 g/cm3

87 Table 2 (continued)

Si: Approved IMA 1983; m3m; NSC = 46; Z = 8; Vc = 160.191 By volcanic exhalations and minor inclusions in Au and Å3; Mc = 224.684 gm; Dc = 1.4026 gm/Å3; Dcalc = 2.33 g/cm3 mantle-derived rocks. Os (Os Ir ): Valid Species (Pre-IMA) 1804; 6/mmm; 0,75 0,25 In magmatic segregation deposits and concentrated in NSC = 26; Z = 2; Vc = 27.519 Å3; Mc = 381.454 gm; placers derived from ultrabasic rocks. Dc = 13.8615 gm/Å3; Dcalc = 23.01 g/cm3 Ru (Ru Ir Os ): Approved IMA 1974; 0,6 0,3 0,1 Placer deposits derived from ultrabasic rocks. Included 6/mmm; NSC = 26; Z = 2; Vc = 27.32 Å3; Mc = 274.660 gm; in rutheniridosmine and in platinum. Dc = 10.0270 gm/Å3; Dcalc = 16.65 g/cm3 Cd: Approved IMA 1979; Found in the heavy non-magnetic fraction of a 6/mmm; NSC = 26; Z = 2; Vc = 43.169 Å3; Mc = 224.822 gm; mechanical concentrate from a gabbro intrusive. Dc = 5.2080 gm/Å3; Dcalc = 8.65 g/cm3 Zn: Valid Species (Pre-IMA) Prehistoric; Oxidized sphalerite, as volcanic exhalations, and in Pt 6/mmm; NSC = 26; Z = 2; Vc = 30.221 Å3; Mc = 130.818 gm; concentrates. Dc = 4.3287 gm/Å3; Dcalc = 7.19 g/cm3 С (Lonsdaleite): Approved IMA 1967; In meteorites. Associated with diamond in diamond- 6/mmm; NSC = 26; Z = 4; Vc = 22.658 Å3; Mc = 48.043 gm; bearing placers. Dc = 2.1204 gm/Å3; Dcalc = 3.52 g/cm3 С (Chaoite): Approved IMA 1969; Occurs in shock-metamorphic graphite gneisses, and in 6/mmm; NSC = 26; Z = 168; Vc = 976.166 Å3; meteorites. Thin lamellae, alternating with graphite. Mc = 2017.798 gm; Dc = 2.0671 gm/Å3; Dcalc = 3.43 g/cm3 С (Graphite-2H): Valid Species (Pre-IMA) Prehistoric; Magmatic, metasomatic, contact- and regional- 6/mmm; NSC = 26; Z = 4; Vc = 35.228 Å3; Mc = 48.043 gm; metamorphic, from С-О-Н fluids. Dc = 1.3638 gm/Å3; Dcalc = 2.26 g/cm3 In: Approved IMA 1979; 4/mmm; NSC = 18; Z = 2; Vc = 52.284 Å3; Mc = 229.636 gm; In greisenized and albitized granite. Dc = 4.3921 gm/Å3; Dcalc = 7.29 g/cm3 Sn: Valid Species (Pre-IMA) Prehistoric; In placer sands (Oban, Australia) and in calcite as 4/mmm; NSC = 18; Z = 4; Vc = 108.190 Å3; Mc = 474.840 gm; discrete grains (Beaverlodge, Canada). Dc = 4.3889 gm/Å3; Dcalc = 7.29 g/cm3 Hg: Valid Species (Pre-IMA) Prehistoric – Secondary mineral resulting from oxidation of cinnabar 3m; NSC = 13; Z = 3; Vc = 68.978 Å3; Mc = 601.770 gm; deposits. Dc = 8.7241 gm/Å3; Dcalc = 14.49 g/cm3 Bi: Valid Species (Pre-IMA) 1500; – Hydrothermal ores of Co, Ni, Ag, and Sn. In pegmatites 3m; NSC = 13; Z = 6; Vc = 211.031 Å3; Mc = 1253.882 gm; and topaz-bearing Sn-W veins. Dc = 5.9417 gm/Å3; Dcalc = 9.87 g/cm3

Sb– : Valid Species (Pre-IMA) Prehistoric 3m; NSC = 13; Z = 6; Vc = 180.060 Å3; Mc = 730.560 gm; Low-temperature mineral in hydrothermal veins. Dc = 4.0573 gm/Å3; Dcalc = 6.74 g/cm3 As: Valid Species (Pre-IMA) Prehistoric; – Low-temperature mineral in ore veins in crystalline 3m; NSC = 13; Z = 6; Vc = 130,014 Å3; Mc = 449,530 gm; rocks. Dc = 3,4576 gm/Å3; Dcalc = 5,74 g/cm3 As (Arsenolamprite): Valid Species (Pre-IMA); 1886; Low-temperature mineral in ore veins in crystalline mmm; NSC = 10; Z = 8; Vc = 177.042 Å3; Mc = 599.373 gm; rocks. Dc = 3.3855 gm/Å3; Dcalc = 5.62 g/cm3 α-S: Valid Species (Pre-IMA) Prehistoric; Volcanic exhalations and bacterial reduction of sulfates mmm; NSC = 10; Z = 128; Vc = 3283.272 Å3; Mc = 4104.320 gm; in sediments. Dc = 1.2501 gm/Å3; Dcalc = 2.08 g/cm3 Te: Valid Species (Pre-IMA) 1783; Hydrothermal vein mineral, associated with native gold, 32; NSC = 9; Z = 3; Vc = 101.302 Å3; Mc = 382.800 gm; and gold and silver tellurides. Dc = 3.7788 gm/Å3; Dcalc = 6.27 g/cm3 Se: Valid Species (Pre-IMA) 1828; Low-temperature (sublimation of fumarolic vapors). 32; NSC = 9; Z = 3; Vc = 81.781 Å3; Mc = 236.88 gm; From selenium-bearing solutions in U and U-V Dc = 2.8965 gm/Å3; Dcalc = 4.81 g/cm3 deposits. As (Pararsenolamprite - As Sb ): IMA 1999; mm2; 0,94 0,05 Overgrowths on colloform arsenic found in dump NSC = 4; Z = 18; Vc = 353.690 Å3; Mc = 1377.252 gm; material in a Sb-As-Ag-Au deposit. Dc = 3.8940 gm/Å3; Dcalc = 6.47 g/cm3 γ-S (Rosickyite): Valid Species (Pre-IMA) 1959; 2/m; NSC = 4; Mc = 4104.320 gm; Found in fumaroles and in hollow limonite nodules. Dc = 1.2029 gm/Å3; Dcalc = 2.00 g/cm3

88 Fig. 1. Relations betweens numbers of elements in the Periodical Table and calculated density of their native minerals

minerals with simple chemical composition certain gen- Analyzing the distribution of the studied minerals eral patterns have been established. with regard to the symmetry systems, it appears that they belong to the following systems (Fig. 2): cubic – 17 minerals (47.22%); Results hexagonal – 7 minerals (19.44%); tetragonal – 2 minerals (5.56%); The minerals in the class of native elements having con- trigonal – 6 minerals (16.67%); secutive or close atomic numbers in the periodic table of orthorhombic – 3 minerals (8.33%); elements form clearly distinct rows in which with the in- monoclinic – 1 mineral (2.78%). crease of the atomic numbers and weights the calculated density of the monoelement minerals decreases (Table 1, Fig. 1). These rows are: 3 C diam (№ = 6, Dcalc = 3.52 g/cm ) – Al (№ = 13, Dcalc = 3 3 2.72 g/cm ) – Si (№ = 14, Dcalc = 2.33 g/cm ) – α-S (№ = 3 16, Dcalc = 2.08 g/cm );

3 Ni (№ = 28, Dcalc = 8.91 g/cm ) – Cu (№ = 29, Dcalc = 3 3 8.93 g/cm ) – Zn (№ = 30, Dcalc = 7.19 g/cm ) – 3 Aspararsenolamprite (№ = 33, Dcalc = 6.47 g/cm ) – Se (№ = 3 34, Dcalc = 4.81 g/cm );

3 Ru (№ = 44, Dcalc = 16.65 g/cm ) – Rh (№ = 45, Dcalc = 3 3 14.59 g/cm ) – Pd (№ = 46, Dcalc = 12.19 g/cm ) – Ag 3 (№ = 47, Dcalc = 10.50 g/cm ) – Cd (№ = 48, Dcalc = 3 3 8.65 g/cm ) – In (№ = 49, Dcalc = 7.29 g/cm ) – Sn (№ = 3 3 50, Dcalc = 7.29 g/cm ) – Sb (№ = 51, Dcalc = 6.74 g/cm ) 3 – Te (№ = 52, Dcalc = 6.27 g/cm );

Os (№ = 76, Dcalc = 23.01) – Ir (№ = 77, Dcalc = 21.45) – Pt (№ = 78, Dcalc = 21.46) – Au (№ = 79, Dcalc = 19.28) – Hg (№ = 80, Dcalc = 14.49) – Pb (№ = 82, Dcalc = 11.34) – Bi (№ = 83, Dcalc = 9.87). Two exceptions of the suggested pattern have been established – Cu and Pt (8.33%), having minimal irregu- Fig. 2. Distribution of 36 studied native minerals within 7 sym- 3 lar differences in the values of Dcalc (g/cm ). metry systems

89 Distributed according to the symmetry categories hexagonal, 6/mmm – 7 (19.44%); (Fig. 3) the same minerals are grouped as follows: high- tetragonal, 4/mmm – 2 (5.56%); – symmetry – 17 (47.22%); intermediate-symmetry – 15 trigonal, 3m – 4 (11.11 %), 32 – 2 (5.56%); (41.67%); and low-symmetry – 4 (11.11%). orthorhombic, mmm – 2 (5.56%), mm2 – 1 (2.78%); The distribution with respect to the crystallographic monoclinic, 2/m – 1 (2.78%). classes with definite values of NSCC is shown in Fig. 4: Native elements crystallizing in symmetry classes cubic, m3m – 17 (47.22%); with definite values of NSCC are shown in Fig. 5.

Fig. 3. Distribution of 36 studied minerals within symmetry Fig. 4. Distribution of 36 studied minerals within symmetry categories classes

Fig. 5. Distribution of native elements according to numbers of symmetry of crystallographic classes (NSCC) and calculated cell densities (gm/Å)

90 33 (or 91.67%) of all 36 monoelement minerals stud- 2) Graphite can also be found as crystal masses ied crystallize in the holohedral classes of the above list- formed by magmatic or volcanic melts (Tsuchiya et al., ed symmetry systems. Thirteen minerals (36.11%) rep- 1991; Kvasnitsa et al., 1999); resent polymorphic modifications. These are distributed 3) Graphite nodules and spheres in meteorites (Ra as follows: kovan and Jaszczak (2002); Fe – 4 polymorphic modifications (with NSCC = 46); 4) Massive polycrystalline vein graphite, as well C – 1 (NSCC = 46) and 3 (NSCC = 26); as well-crystallized graphite crystals and spherulites in As – 1 (NSCC = 13), 1 (NSCC = 10) and 1 (NSCC = 9); metamorphic or magmatic rocks, can precipitate from α-S (NSCC = 10) and γ-S (NSCC = 4). epigenetic C-O-H fluids (Rumble et al., 1986; Luque et 12 polymorphic modifications (92.31%) also crystal- al., 1998; Pasteris, 1999); lize in the holohedral classes on the respective symmetry 5) The graphite mineralizations can also be pseudo- systems (Table 2, Fig. 4). morphic after diamond as those found in Morocco and South Spain (Pearson et al., 1989); 6) Graphite can be present in metamorphic rocks OCCURRENCE AND GENESIS (gneisses, schists and marbles) as flake-like and deformed OF MONOELEMENT MINERALS crystals (Kretz, 1996), well developed and well shaped crystals (Palache, 1941) or smooth spheres (Jaszczak and The native elements having the lowest atomic numbers Robinson, 2000). The isotopic data suggest that graphite in the periodic table, as well as the lowest calculated in meta-sedimentary rocks forms during the metamor- densities of their minerals, are C, Al, Si, and S. Three of phism of organic matter (Weiss et al., 1981; Kitchen and them (C, Al, S) are polygenic and two (С and S) form Valley, 1995). polymorphic modifications at different thermodynamic Diamond and graphite are the best studied carbon conditions. Native As and Fe also form polymorphic polymorphs. Polymorphic transitions exist among them modifications, but have significantly higher values of at certain thermodynamic conditions as intermediate 3 3 both Dc (gm/Å ) and Dcalc (g/cm ). phases can also form (Akaishi et al., 1990; Gogotsi et al., 1998, 1999; Leech and Ernst, 1998; Chen et al., 1999; Carbon Fayos, 1999; Sato et al., 1999; El Goresy et al., 2001; Ewels et al., 2001; Kenkmann et al., 2002; Willems et Four polymorphs of carbon were identified in nature: al., 2004). hexoctahedral diamond (NSCC = 46) and dihexa gonal-dipyramidal lonsdaleite, chaoite and graphite Aluminum (NSCC = 26). Beside the well known magmatic diamond de- Different geological processes can lead to formation of posits in kimberlites, microdiamonds formed under native aluminum: ultrahigh-pressure metamorphic conditions were also 1) Native Al (m3m, NSCC = 46) was found in xeno- established (Sobolev and Shatsky, 1990; Dobrzhi liths of eclogites and different ultrabasic rocks found in netskaya et al., 1995, 2003; De Korte et al., 2000; kimberlites from Siberian diamond deposits. These con- Nasdala and Massonne, 2000; El Goresy et al., 2001; ditions suggests Al formation in association with other Mposkos and Kostopulos, 2001; Stoeckhert et al., native phases and alloys, such as Fe, Ni, Cu, Zn, Pb, Sb, 2001; Bostick et al., 2003; Chopin, 2003; Ishida et al., Sn, Mn, Au, Si, C in kimberlite breccias (Kovalskiy et 2003; Yang et al., 2003; Perraki et al., 2004, 2006; al., 1981; Kovalskiy and Oleynikov, 1983, 1985); Nasdala et al., 2005). 2) Grains of Al and other native elements (Fe, Cu, Zn, Lonsdaleite is defined as a separate mineral species Pb, Sn, Cd and C-graphite), alloys (CuZn, SnSb) and car- representing hexagonal modification of carbon (Bundy bides of Fe and Si were found in basic rocks (anorthosite and Kasper, 1967; Frondel and Marvin, 1967; Hanneman and picrite gabbro-dolerite) from the Siberian Platform. et al., 1967; Kaminskiy et al., 1985; Cheim et al., 2003). The basaltic melt evolved in reductive environment It forms at PT conditions similar to those of diamond, at pressure of 15 kbar and temperature 1440–1550 °C and was also established in meteorites. (Oleynikov et al., 1978; Oleynikov, 1979). The crystal- Chaoite is the less-known modification of the carbon. lization of the native Al in basic and ultrabasic rocks

It results from shock metamorphism of graphite-bearing results from interaction of SiO2-undersaturated magma gneisses (El Goresy and Donnay, 1968). containing normative Al2O3 with host rocks or fluids Graphite is the most widespread polymorphic mod- bearing NaCl and SiO2. The precipitation of native Al ification of carbon in nature. Summarizing the data of occurs when temperature decreases in faults in the pres- previous authors, Rakovan and Jaszczak (2002) systema- ence of reduction gases (Osadchiy and Alehin, 1984). tize the forms of appearance of graphite mineralizations 3) High-temperature magma fluids lead to precipi- found in nature according to their genesis: tation of sublimate mineral associations of native ele- 1) Graphitized masses resulting from solid-state ments such as Al, Au, Pt, Si, Ti, Mo, Cr, Sn, Cu, Ag, Se transformation of sediments rich in organic matter. They in the fumarolic fields of the active Kudryaviy Volcano show significant variations in their chemical composi- (Kurile Islands) (Korzhinski et al., 1996; Yudovskaya tion and the degree of crystal lattice perfection (Buseck et al., 2006); and Huang, 1985; Pasteris and Wopenka, 1991; Bustin 4) Native Al was found in phlogopite-plagioclase et al., 1995); lenses in desilificated pegmatite vein together with

91 phlogopite, halloysite, apatite, chrysoberyl and emerald The minerals of the native elements crystallizing in (Arnaudov, 2006; Dekov et al., 2009); the dihexagonal-dipyramidal class (6/mmm) with NSCC 5) Native Al also forms under low-temperature con- = 26 result from magmatic, contact- and regional meta- ditions. It was identified in mercury and antimony ore morphic processes or from impact metamorphism and deposits (Kupenko and Osadchiy, 1981; Blohina, 1982), volcanic exhalations. The native zinc only forms by oxi- in pyrite-polymetallic ores (Alehina et al., 1983), in dation of sphalerite (Table 2). gibbsite-alunite-halloysite rocks (Dombrovskaya et al., The native indium and tin crystallize in the dite- 1984); in the Ukchilkan tin deposits in the Northeastern tragonal-dipyramidal class (4/mmm) with NSCC = 18. Yakutia (Stoliyarov et al., 1988). Aluminum was found Compared with the minerals from the above mentioned in the voids in fluidal rhyolites (Filimonova and Trubkin, groups they form under lower-temperature conditions 1996), in buried wood in brown coal deposit (Seredin and (Table 2) Magazina, 1999); The native minerals of Hg, Bi, Sb and As crystallize – 6) Native Al was found in the deep-sea terrigenous- in trigonal-scalenohedral class (3m) and have NSCC = pyroclastic sediments (Shterenberg and Vasilieva, 1979), 13. Native bismuth occurs in pegmatites and hydrother- in modern pelagic sediments, in Fe-Mn concretions from mal veins. Antimony and arsenic are products of low- marine sediments containing ore minerals (Shterenberg, temperature hydrothermal fluids. Mercury is a secondary 1981; Baturin et al., 1984; Iushko-Zakharova et al., mineral resulting from oxidation of cinnabar (Table 2). 1984; Shterenberg et al., 1986, Shnyukov et al., 1987; Arsenolamprite (polymorph of native arsenic) and Butuzova et al., 1987; Arsamakov et al., 1988; Dekov α-sulfur belong to the orthorhombic-dipyramidal class et al., 1993, 1995). (mmm) with NSCC = 10. Arsenolamprite is a low-temperature hydrothermal mineral. The rhombic α-sulfur is Silicon, Sulfur, Chromium, Iron and Arsenic either a volcanic exhalative product or results from bacterial reduction of sulfates in sediments (Table 2). The native silicon (m3m, NSCC = 46) is related to vol- The trigonal tellurium and selenium crystallize in canic exhalations. It was also found as micro-inclusions class 32 and have NSCC = 9. Native tellurium is a hy- in native gold, as well as in derivates of mantle rocks. drothermal vein mineral. Native selenium is a low-tem- The polymorphs of the native sulfur (mmm, NSCC perature hydrothermal phase and can also be fumarol in = 10 and 2/m, NSCC = 4) result from volcanic exhala- origin (Table 2). tions but they may also form during bacterial reduction Pararsenolamprite is orthorhombic, crystallizing in of sulfide minerals in sediments. They were also found in class mm2. The monoclinic sulfur belongs to the holo- the pores of limonite concretions (http://www.webmin- hedral class 2/m. The both classes have NSCC = 4. eral.com). The genesis and IMA status of the two sulfur Pararsenolamprite is a low-temperature phase growing polymorphs are reported in Table 2. over colomorphic arsenic. The monoclinic sulfur is a Native chromium (m3m, NSCC = 46) was established fumarolic product or can be found in voids in limonite in the heavy fraction separated from the contact zone be- concretions (Table 2) tween silicate minerals containing marbles and ultrabasic rocks (http://www.webmineral.com). The polymorphic modifications of the native iron Conclusions (m3m, NSCC = 46) most often form in the temperature range between 700 and 1400o C (Table. 2) in association Analyzing the data reported above, the following conclu- with other native elements such as Al, Cu, Zn, Pb, Sn, sions can be drawn: 3 3 Cd, C (Oleynikov et al., 1978; Oleynikov, 1979; Kostov, The values of the densities Dc (gm/Å ) and Dcalc (g/cm ) 1993). Native Fe and Al were established in berried iron- of the monoelement minerals decrease with the increase manganese concretions from the Chain transform fault, of atomic weight of native elements with consecutive or Atlantic Ocean (Shnyukov et al., 1987). close atomic numbers. – Native arsenic (3m, NSCC = 13; mmm, NSCC = The values of NSCC show a general tendency to de- 10; and mm2, NSCC = 4) is a typical low-temperature crease with decreasing of temperature and pressure of mineral, associating with silver, realgar, stibnite, ga- formation of the monoelement minerals. The monoelement polymorphic modifications of As lena, etc. Most often it transforms into arsenolite As2O3 (Kostov, 1993). and S, crystallizing in the low-symmetry crystal systems, are exceptions of Groth’s law. They occur as exhalative products, in low-temperature hydrothermal and DISCUSSION exogenic systems. 3 At certain NSCC values, the highest the Dc (gm/Å ) 3 The most of 36 studied minerals are hexoctahedral and Dcalc (g/cm ) of the monoelement minerals, the less (m3m) with NSCC = 46. They normally form under probable their polymorphic modifications are to be magmatic, contact-metamorphic, pegmatitic, and hy- established. drothermal conditions or result from volcanic exhala- Polymorphic modifications denser than α-iron (hav- 3 3 tions. Native copper can only form in supergenic envi- ing Dc = 4.7049 gm/Å and Dcalc = 7.81 g/cm ) have not ronment. Native aluminum was established in magmatic been established. rocks and pegmatites, as well as in deep-sea sediments In 94.44% of cases, with increase of the NSCC val- and concretions (Table 2). ues, the number of the monoelement minerals, crystal-

92 lizing in the respective symmetry classes also increases. highest values of NSCC in the respective systems. The The only exceptions are the minerals belonging to the quantitative integral characteristics NSCC is therefore ditetragonal-dipyramidal class (4/mmm) with NSCC = informative not only for the polymorphic modifications 18. Their number seems irregularly lower. and minerals with simple chemistry but is also applicable The largest part (91.67%) of the monoelement miner- in studies of all kinds of mineral assemblages grouped als crystallize in the holohedral classes. From the previ- using different characteristics. ously studied 113 polymorphic minerals, composed by one to five elements, 94 (83.18%) crystallize in the holo- Acknowledgements hedral classes, too (Vlahov, 2010). The crystallographic classes of 4106 mineral species are known. 2932 of them The author thanks to the reviewers Ognyan Petrov (71.41%) also crystallize in the holohedral classes of (Institute of Mineralogy and Crystallography, BAS, Sofia) the different systems. These facts suggest that mineral and Ruslan Kostov (University of Mining and Geology, species in general prefer holohedral classes, having the Sofia) for their critical suggestions and comments.

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