Heyerdahlite, Na3Mn7Ti2(Si4O12)2O2(OH)4F(H2O)2, a new mineral of the astrophyllite supergroup from the Larvik Plutonic complex, Norway: Description and crystal structureELENA SOKOLOVA ET AL.DESCRIPTION AND CRYSTAL STRUCTURE OF HEYERDAHLITE

Heyerdahlite, ideally Na 3 Mn 7 Ti 2 (Si 4 O 12 ) 2 O 2 (OH) 4 F(H 2 O) 2 , is a new astrophyllite-supergroup mineral from the Larvik Plutonic complex, Norway. Heyerdahlite was found in a nepheline-syenite pegmatite with albite, aegirine, hastingsite/magnesio-hastingsite, kupletskite, lorenzenite and pyrophanite. Heyerdahlite is colourless to pale brown, transparent and has a vitreous lustre. Mohs hardness is 3, D calc. = 3.245 g/cm 3 . Heyerdahlite is biaxial (+), α = 1.694(2), β = 1.710(5), γ = 1.730(5), 2V meas. = 80(4)° and 2V calc. = 84.5°. Cleavage is perfect parallel to {001}. The empirical formula based on 32.18 (O + F) apfu is (Na 1.18 K 0.68 Rb 0.12 Cs 0.01 Pb 0.01 ) Σ2 Na 1.00 (Mn 6.29 Zn 0.23 Mg 0.07 Zr 0.04 ${\rm Fe}_{{\rm 0}{\rm. 03}}^{{\rm 2 +}} $ Ca 0.01 Na 0.34 ) Σ7.01 (Ti 1.78 Nb 0.17 Mg 0.03 Zr 0.02 ) Σ2 (Si 8.03 O 24 )O 2 [(OH) 3.92 F 0.08 ] Σ4 F 1.00 [(H 2 O) 1.18 □ 0.82 ] Σ2 , for Z = 1. Heyerdahlite is triclinic, space group P $\bar 1$ , a = 5.392(2), b = 11.968(4), c = 11.868(4) A, α = 112.743(8), β = 94.816(7), γ = 103.037(8)° and V = 675.6(7) A 3 . The crystal structure was refined to R 1 = 4.44% for 3577 unique ( F o > 4σ F ) reflections. In the crystal structure of heyerdahlite, there are four [4] T sites occupied by Si. The [6] D site is occupied mainly by Ti. The T 4 O 12 astrophyllite ribbons composed of SiO 4 tetrahedra and D octahedra constitute the H (Heteropolyhedral) sheet. In the O (Octahedral) sheet, there are four Mn-dominant [6] M (1–4) sites. Two H sheets and one central O sheet form the HOH block, and adjacent HOH blocks link via a common ${\rm X}_{\rm D}^{\rm P} $ anion of the two D octahedra. In the I (Intermediate) block between HOH blocks, there are two interstitial cation sites, A and B , and a W A site, partly occupied by H 2 O. The A site splits into two sites, [12] A (1) and [6] A (2), partly occupied by K and Na, respectively, with A(1)–A(2) = 0.754 A. The aggregate content of the A site is ideally Na 2 apfu. The [10] B site is occupied by Na. The W A site is ideally occupied by (H 2 O) 2 pfu. The mineral is named after the Norwegian explorer Thor Heyerdahl (1914–2002), who was born in Larvik.