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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

Lo straordinario incrementodi nuovi minerali della tormalina negli ultimi tre anni

Ferdinando Bosi

Dipartimento di Scienze della Terra, Sapienza Università di Roma

slide2

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.

slide3

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)

slide4

Tourmaline is interesting…

– as a mineral

– as a gemstone

–as a petrological indicator

– as a material for technological applications

slide5

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).

slide6

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.

slide7

as a gemstone

Tourmaline gem varieties are often known on color basis

Rubellite(rose, dark pink, to red)

slide8

as a gemstone

Verdelite (green to yellow-green)

slide9

as a gemstone

Indicolite (blue to blue-green)

slide10

as a gemstone

Achroite(colorless)

slide11

as a gemstone

Canary tourmaline (yellow)

slide12

as a gemstone

Chrome tourmaline (vivid green)

slide13

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)

slide14

as a gemstone

Cat’s eye and moor’s head tourmalines

slide15

as a gemstone

As tourmalines are sensitive to physicochemical

changes in their growth environment, they may be optically zoned.

slide16

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

slide17

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

slide18

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

slide19

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

slide20

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.

slide21

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.

slide22

as a mineral

The tourmaline structure

XY3Z6(T6O18)(BO3)3V3W

“X+Y+B+T”

Structural islands

slide23

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

slide24

as a mineral

The tourmaline structure

Projected onto (0001)

slide25

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.

slide26

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

slide27

as a mineral

The 3-D framework of ZO6 must be able to accommodate the structural islands

slide28

as a mineral

Spatial relationships and reciprocal constraints of ZO6 and YO6:

the islands made of 3 Y are surrounded by continuous Z skeleton

slide29

as a mineral

As YO6 is larger than ZO6, there is mismatch between these two non-equivalent distorted octahedra

Structural constraints on chemical variability

slide30

as a mineral

Long-range constraints

254 data from SREF

So far…

slide31

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

slide32

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

slide33

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

slide34

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)

slide38

Nomenclature

Tourmaline classification (Henry et al. 2011)

slide39

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 !

slide40

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)

slide41

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)

slide42

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)

slide43

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

slide44

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)

slide45

Oxy-tourmalines

Oxy-chromium-dravite

Oxy-vanadium-dravite

Vanadio-oxy-chromium-dravite

Vanadio-oxy-dravite

Chromo-alumino-povondraite

slide46

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)

slide47

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

“Intermediate" end-members

slide48

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

slide49

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

slide50

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

?

slide51

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

Confirmed by

a systematic study

(work in progress)

Site preference:

YV > YCr > YAl

ZAl> ZCr> ZV

slide52

Nomenclature

(Henry et al. 2013)

“In the absence of specific structural information on the Y- and Z-site occupancies, a procedure is recommended for allocating cations to Z and Y ... Initially assign all Al3+ (in excess of that assigned to T) to the Z site. Next, successively assign Mg2+ (up to 2 apfu), V3+, Cr3+, and Fe3+. If there is an excess of trivalent cations on Z, it goes into Y”.

Chemical analysis, sample PR1973

(Na ~1 apfu, Mg ~2, V3+ ~2.2, Cr ~3.8 , Al ~1, Si ~6, B = 3, OH ~3)

Recommended formula according to Henry et al. (2013):

NaY(Cr3)Z(Al1Mg2V2.2Cr0.8)(Si6O18)(BO3)3(OH)3W(O)

Empirical formula according to the structural information:

NaY(Cr0.8V2.2)Z(Al1Mg2Cr3)(Si6O18)(BO3)3(OH)3W(O)

slide53

Nomenclature

(Henry et al. 2013)

“In the absence of specific structural information on the Y- and Z-site occupancies, a procedure is recommended for allocating cations to Z and Y ... Initially assign all Al3+ (in excess of that assigned to T) to the Z site. Next, successively assign Mg2+ (up to 2 apfu), V3+, Cr3+, and Fe3+. If there is an excess of trivalent cations on Z, it goes into Y”.

Chemical analysis, sample PR1973

(Na ~1 apfu, Mg ~2, V3+ ~2.2, Cr ~3.8 , Al ~1, Si ~6, B = 3, OH ~3)

Recommended formula according to Henry et al. (2013):

NaY(Cr3)Z(Al1Mg2V2.2Cr0.8)(Si6O18)(BO3)3(OH)3W(O)

Empirical formula according to the structural information:

NaY(Cr0.8V2.2)Z(Al1Mg2Cr3)(Si6O18)(BO3)3(OH)3W(O)

slide54

Nomenclature

(Henry et al. 2013)

“In the absence of specific structural information on the Y- and Z-site occupancies, a procedure is recommended for allocating cations to Z and Y ... Initially assign all Al3+ (in excess of that assigned to T) to the Z site. Next, successively assign Mg2+ (up to 2 apfu), V3+, Cr3+, and Fe3+. If there is an excess of trivalent cations on Z, it goes into Y”.

Chemical analysis, sample PR1973

(Na ~1 apfu, Mg ~2, V3+ ~2.2, Cr ~3.8 , Al ~1, Si ~6, B = 3, OH ~3)

Recommended formula according to Henry et al. (2013):

NaY(Cr3)Z(Al1Mg2V2.2Cr0.8)(Si6O18)(BO3)3(OH)3W(O)

Empirical formula according to the structural information:

NaY(Cr0.8V2.2)Z(Al1Mg2Cr3)(Si6O18)(BO3)3(OH)3W(O)

Vanadio-oxy-chromium-dravite

X(Na)Y(V)3Z(Mg2Cr4)T(Si6O18)(BO3)3V(OH)3W(O)

slide55

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

Boundaries within the diagram?

slide56

Ternary diagram for V-Cr-Al oxy-tourmaline in accord with the recommendations of Henry et al. (2013), except for V3+ and Cr3+

1) Y(Al1Cr1V1)Z(Al4Mg2)

2) Y(Cr1.5V1.5)Z(Al4Mg2)

3) Y(Cr1.5V1.5)Z(Cr2Al2Mg2)

4) Y(V3)Z(Cr2Al2Mg2)

5) Y(V3)Z(V1.33Cr1.33Al1.33Mg2)

slide57

Ternary diagram for V-Cr-Al oxy-tourmaline in accord with the recommendations of Henry et al. (2013), except for V3+ and Cr3+

slide58

Ternary diagram for V-Cr-Al oxy-tourmaline in accord with the recommendations of Henry et al. (2013), except for V3+ and Cr3+

NaY(Cr1.4V1.6)Z(Mg2Cr1.9Al2.1)(Si6O18)(BO3)3(OH)3O

Crtot= 3.3 > Altot = 2.1 > Vtot = 1.6

Vanadio-oxy-dravite

slide60

Coming soon…

Special Collection on Spinels in American Mineralogist

Spinels Renaissance:

The past, present and future of those ubiquitous materials

A special collection, focused on diverse topics, related to the structure, properties and applications of natural and synthetic spinels and spinelloids on bulk and nanoscale. The section aims at the revival of the interest in the spinel materials at present and particularly on the promising future of the non-oxygen containing and nanosized structures. We hope to bring together experimental and theoretical research studies from mineralogists, geologists, chemists, materials scientists, physicists and crystallographers.

Papers will undergo normal peer review, conducted by special collection associate editors Kristina Lilova, Kaimin Shih and Ferdinando Bosi.