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Lo straordinario incremento di nuovi minerali della tormalina negli ultimi tre anni

Lo straordinario incremento di nuovi minerali della tormalina negli ultimi tre anni. Ferdinando Bosi Dipartimento di Scienze della Terra, Sapienza Università di Roma. Tourmalines are borosilicates represented by the general formula: XY 3 Z 6 (T 6 O 18 )(BO 3 ) 3 V 3 W.

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Lo straordinario incremento di nuovi minerali della tormalina negli ultimi tre anni

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  1. Lo straordinario incrementodi nuovi minerali della tormalina negli ultimi tre anni Ferdinando Bosi Dipartimento di Scienze della Terra, Sapienza Università di Roma

  2. Tourmalines are borosilicates represented by the general formula: XY3Z6(T6O18)(BO3)3V3W [9]X = Na, K, Ca, vacancy; [6]Y = Al, Cr, V, Fe, Mg, Mn, Li etc. ; [6]Z = Al, Cr, V, Fe, Mg; [4]T = Si, Al, B; [3]B = B; [3]W(O1) = OH, F, O; [3]V(O3) = OH, O. Tourmalines occur in a wide variety of sedimentary, igneous, and metamorphic rocks.

  3. The best-known species probably are: Dravite NaMg3Al6(Si6O18)(BO3)3(OH)3(OH) Schorl NaFe3Al6(Si6O18)(BO3)3(OH)3(OH) Elbaite Na(Al1.5Li1.5)Al6(Si6O18)(BO3)3(OH)3(OH)

  4. Tourmaline is interesting… – as a mineral – as a gemstone –as a petrological indicator – as a material for technological applications

  5. as a gemstone Tourmaline was “discovered” as a gemstone. In fact, the term tourmaline seems to be derived from the Sinhalese word turmali, which was used to refer to mixed-colored stones of unknown type by gem dealers in Ceylon (now Sri Lanka).

  6. as a gemstone “Mother Nature’s rainbow” Gem tourmaline is famous for its extensive range of colors, even within individual crystals: from colorless, through red, pink, yellow, orange, green, blue, and violet, to brown and black.

  7. as a gemstone Tourmaline gem varieties are often known on color basis Rubellite(rose, dark pink, to red)

  8. as a gemstone Verdelite (green to yellow-green)

  9. as a gemstone Indicolite (blue to blue-green)

  10. as a gemstone Achroite(colorless)

  11. as a gemstone Canary tourmaline (yellow)

  12. as a gemstone Chrome tourmaline (vivid green)

  13. as a gemstone Paraíba-type (“neon” blue-to-green) is one of the highest-priced colored gemstones (values comparable to those of some diamonds, Pezzottaand Laurs 2011)

  14. as a gemstone Cat’s eye and moor’s head tourmalines

  15. as a gemstone As tourmalines are sensitive to physicochemical changes in their growth environment, they may be optically zoned.

  16. as a gemstone Cut stones are often mounted into jewelry Pendant consisting of two Cu-bearing tourmalines (10.95 ct pink and 6.95 ct yellow) set in 18 k gold with diamonds

  17. as a mineral Tourmaline structure is one of the most complex as well as the most elegant of all crystal structures of rock-forming minerals

  18. as a mineral The tourmaline structure XY3Z6(T6O18)(BO3)3V3W T-site The cyclosilicate structure is formed by rings of six TO4 tetrahedra, which point in the same direction. Thus, the structure results both noncentrosymmetric and polar: thus, tourmaline is both piezoelectric and pyroelectric

  19. as a mineral The tourmaline structure XY3Z6(T6O18)(BO3)3V3W X-site Tourmaline supergroupcan be classified into primary groups based on the dominant occupancy of the Xsite: vacant, alkali and calcic groups. This grouping makes sense because X-site occupancy usually reflects the paragenesis of the rock in which these tourmalines crystallize

  20. as a mineral The tourmaline structure XY3Z6(T6O18)(BO3)3V3W Y-site The most extensive compositional variation occurs at the Y site. Y-site is able to incorporate cations of different sizes and charges, including vacancies.

  21. as a mineral The tourmaline structure XY3Z6(T6O18)(BO3)3V3W B-site Boron makes tourmaline one of the most important boron-bearing minerals (reservoir of B) in the Earth’s crust.

  22. as a mineral The tourmaline structure XY3Z6(T6O18)(BO3)3V3W “X+Y+B+T” Structural islands

  23. as a mineral The tourmaline structure XY3Z6(T6O18)(BO3)3V3W Z-site ZO6 octahedra link the structural islands The 3-D framework is given by ZO6

  24. as a mineral The tourmaline structure Projected onto (0001)

  25. as a mineral The tourmaline structure The 3-D framework of ZO6 explains the tourmaline hardness (7-7½ Mohs) and lack of cleavage, making tourmaline a resistant mineral in clastic sediments.

  26. as a mineral Tourmaline structure can accommodate a large range of chemically different elements: XY3Z6(T6O18)(BO3)3V3W [9]X = Na, Ca, Vac. >> K, Pb, Ag [6]Y = Al, Cr, V, Fe3+, Fe2+, Mg, Mn3+, Mn2+, Li >> Ti, Zn, Cu, Ni, Co, Vac., etc. [6]Z = Al, Cr, V, Fe3+ > Mg, Fe2+ [4]T = Si >> Al, B, Be [3]B = B [3]W(O1) = OH, F, O [3]V(O3) = OH, O But its crystal chemistry is controlled by structural constraints

  27. as a mineral The 3-D framework of ZO6 must be able to accommodate the structural islands

  28. as a mineral Spatial relationships and reciprocal constraints of ZO6 and YO6: the islands made of 3 Y are surrounded by continuous Z skeleton

  29. as a mineral As YO6 is larger than ZO6, there is mismatch between these two non-equivalent distorted octahedra Structural constraints on chemical variability

  30. as a mineral Long-range constraints 254 data from SREF So far…

  31. as a mineral Long-range dimensional constraints Order-disorder reaction YAl3+ + ZMg2+ → YMg2++ ZAl3+ applies to the tourmaline to reduce the misfit between <Y-O> and <Z-O>. By the incorporation of smaller cations (R3+) into Y and larger cations (R2+) into Z, <Y-O> decreases and <Z-O> increases

  32. Tourmaline classification The general formula: XY3Z6(T6O18)(BO3)3V3W [9]X = Na, K, Ca, vacancy; [6]Y = Al, Cr, V, Fe, Mg, Mn, Li etc. ; [6]Z = Al, Cr, V, Fe, Mg; [4]T = Si, Al, B; [3]B = B; [3]W(O1) = OH, F, O; [3]V(O3) = OH, O. The dominanceof theseionsatone or more sites of the structuregivesrise to a rangeof distinct mineral species

  33. Tourmaline is, in fact, not a single mineral but a supergroup currently consisting in 27 species approved by IMA-CNMNC

  34. The last 3 years have seen an amazing increase in tourmaline species: 17 + 10 = 27 IMA-ACCEPTED TOURMALINE SPECIES From Henry et al. (2011) 1 – Dravite 2 – Schorl 3 – Elbaite 4 – Fluor-dravite 5 – Fluor-schorl 6 – Povondraite 7 – Rossmanite 8 – Fluor-buergerite 9 – Olenite 10 – Uvite 11 – Fluor-uvite 12 – Feruvite 13 – Fluor-liddicoatite 14 – Foitite 15 – Magnesio-foitite 16 – Chromo-alumino-povondraite 17 – Chromium-dravite 18 – Oxy-schorl(Bačik et al., IMA 2011-011) 19 – Tsillaisite(Bosi et al., IMA 2011-047) 20 – Fluor-elbaite(Bosi et al., IMA 2011-071) 21 – Oxy-chromium-dravite(Bosi et al., IMA 2011-097) 22 – Oxy-vanadium-dravite(Bosi et al., IMA 2012 11-E) 23 – Oxy-dravite (Bosi et al., IMA 2012-004a) 24 – Darrellhenryite(Novák et al., IMA 2012-026) 25 – Vandio-oxy-chromium-dravite (Bosi et al., IMA 2012-034) 26 – Fluor-tsilaisite(Bosi et al., IMA 2012-044) 27 – Vanadio-oxy-dravite (Bosi et al., IMA 2012-074)

  35. Nomenclature Tourmaline classification (Henry et al. 2011)

  36. Tourmaline classification of Henry et al. (2011, 2013) XY3Z6(T6O18)(BO3)3V3W “For the purposes of classification of tourmaline species, actual tourmaline structural information of the Y- and Z-site occupancy is an overriding consideration for the definition of a tourmaline species” Henry et al. (2013). Empirical (real) structural formula has to be used in naming the tourmaline Hence, accurate site allocation of cations and anions is needed !

  37. Empirical structural formula of Clark et al. (2011): XNaY(Mg2+1.4Al3+0.6Fe2+)Z(Al3+5.4Mg2+0.6)T(Si6O18)B(BO3)3V(OH)3W[F0.7(OH)0.3] Fluor-dravite, end-member formula NaY(Mg3)Z(Al6)(Si6O18)(BO3)3(OH)3(F)

  38. Structural formula: Na Y(Fe2+1.4Mg1.6-xAlx) Z(MgxAl6-x) (Si6O18)(BO3)3(OH)3F x < 0.2 (for example, x = 0.1) Y(Fe2+1.4Mg1.5Al0.1) Z(Mg0.1Al5.9)

  39. Structural formula: Na Y(Fe2+1.4Mg1.6-xAlx) Z(MgxAl6-x) (Si6O18)(BO3)3(OH)3F x > 0.2 (for example, x = 0.3) Y(Fe2+1.4Mg1.3Al0.3) Z(Mg0.3Al5.7)

  40. Nomenclature Structural formula: Na Y(Fe2+1.4Mg1.6-xAlx) Z(MgxAl6-x) (Si6O18)(BO3)3(OH)3F x < 0.2, fluor-dravite x >0.2, fluor-schorl For the same bulk chemistry, the name changes as a function of the degree of order/disorder over Y and Z

  41. Oxy-tourmalines Oxy-chromium-dravite X(Na)Y(Cr)3Z(Cr4Mg2)T(Si6O18)(BO3)3V(OH)3W(O) Oxy-vanadium-dravite X(Na)Y(V)3Z(V4Mg2)T(Si6O18)(BO3)3V(OH)3W(O) Vanadio-oxy-chromium-dravite X(Na)Y(V)3Z(Cr4Mg2)T(Si6O18)(BO3)3V(OH)3W(O) Vanadio-oxy-dravite X(Na)Y(V)3Z(Al4Mg2)T(Si6O18)(BO3)3V(OH)3W(O) Chromo-alumino-povondraite X(Na)Y(Cr)3Z(Al4Mg2)T(Si6O18)(BO3)3V(OH)3W(O) Oxy-dravite X(Na)Y(Al)3Z(Al4Mg2)T(Si6O18)(BO3)3V(OH)3W(O)

  42. Oxy-tourmalines Oxy-chromium-dravite Oxy-vanadium-dravite Vanadio-oxy-chromium-dravite Vanadio-oxy-dravite Chromo-alumino-povondraite

  43. The 5 new species of Cr-V-oxy-tourmalines occur in the Pereval marble quarry, near the town of Sludyanka (51°37′N 103°38′E), Irkutsk region, Southern Lake Baikal, Siberia, Russia The Sludyanka complexcomprisesedimentary-metamorphicrocksconsisting of diverse gneisses, carbonate, and carbonate-silicaterocks and maficschists Probably, Cr-V-oxy-tourmalines were formed in the prograde stage of metamorphism (i.e., granulite facies)

  44. Ternary diagram for V-Cr-Al oxy-tourmaline NaYR3+3Z(R3+4Mg2)(Si6O18)(BO3)3(OH)3O “Intermediate" end-members

  45. What are their compositional fields in the diagram V-Cr-Al? Example, chromo-alumino-povondraite: it is between oxy-chromium-dravite and oxy-dravite join. Crtot= 5.0 and Altot= 2.0 Crtot = 3.0 and Altot= 4.0 Crtot= 1.5 and Altot= 5.5 ZCr2↔ZAl2 YCr1.5↔YAl1.5

  46. Ternary diagram for V-Cr-Al oxy-tourmaline NaYR3+3Z(R3+4Mg2)(Si6O18)(BO3)3(OH)3O

  47. Ternary diagram for V-Cr-Al oxy-tourmaline NaYR3+3Z(R3+4Mg2)(Si6O18)(BO3)3(OH)3O Site preference: YV > YCr > YAl ZAl> ZCr> ZV ?

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