Paolo Conti

Samos Training School, 26-30 August 2013

conti@unisi.it

Microstructures, textures and material properties

of marble rocks

, Italy

• Marble behaviour• Crystal structure of minerals and rocks• Rock fabrics• Marble deterioration• Mechanical properties• Natural examples

2

Contents

Marbles: different behaviour

3(from Shushakova et al., 2010)(Ephesus, Turkey)

Marbles: different behaviour

4

panels

Marbles: different behaviour

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Marbles

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Same composition (≃100 % CaCO3)

Different behaviour due to:• anisotropic physical properties of calcite crystals• texture of rocks• microstructure of rocks

Anisotropic physical properties:Crystal structure of rocks

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Anisotropic physical properties: strength

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crystal“weak”bond

“strong”bond

Anisotropic physical properties: strength

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crystal“weak”bond

“strong”bond

Anisotropic physical properties:thermal expansion

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Increasing temperature: stretch of bond length “weak”

bond

“strong”bond

Anisotropic physical properties:thermal expansion

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(Winkler, 1994)

Anisotropic physical properties:natural texture

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crystallographicdirection

(a) (b) (c) (d) (e)

strong crystallographicpreferred orientation

weak crystallographicpreferred orientation

Anisotropic physical properties: shapes

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(Ruedrich et al., 2011)

Along grain buondaries, weatering: micro-karst, breakouts, coloration, formation of crusts, biological colonization, granular desintegration, peeling, moisture expansion, etc.Superficial disintregration - loss of cohesion (dilatancy) - total decay of the material

Anisotropic physical properties: shapes

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straight grain boundaries

lobate grain boundaries

“slide” “locked”

Anisotropic physical properties: shapes

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shape preferred orientation of crystals

no shape preferred orientation of crystals

(anisotropic volume increase)

Developement of microstructures (movies)

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dynamic(syn-tectonic)

recrystallization

staticrecrystallization

(annealing)

Octachloropropane (organic material)Means et al. (1994) J. Struct. Geol.,16, 403-418

before:no shape preferred orientation, straight grain boundaries

before:shape preferred orientation, lobate grain boundaries

http://www.atmos.albany.edu/geology/webpages/wdmovies/wdmoviep.html

Anisotropic physical properties

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(a) (b) (c) (d) (e)

•no shape preferred orientation of grains

•no crystallographic preferred orientation

•no shape preferred orientation of grains

•crystallographic preferred orientation

•shape preferred orientation of grains

•no crystallographic preferred orientation

•shape preferred orientation of grains

•crystallographic preferred orientation

crystallographic preferred orientation of crystals = texture of rockshape preferred orientation of crystals = microstructure of rock

(texture + microstructure = fabric)

In marbles...

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limited informations from outcrop studies only

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Microstructures in marbles“ultra” thin section (

Microstructures in marbles

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(Carmignani, Conti, et al., 2007)

Carrara marble (Italy)

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Microstructures in marbles: measure

(Molli, Conti et al., 2007)

Textures in marbles: measure

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(same color, same crystallographic orientation)

(Molli, Conti et al., 2007)

CIP analysis(Heilbronner Panozzo R. & Pauli C. (1993) - Integrated spatial and orientation analysis of quartz c-axis by computer-aided microscopy. Journal of Structural Geology, 13, 369–382.)

In marble rocks ...

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• Physical properties of rock linked with texture and microstructure;

• Laboratory studies yield informations about rock texture and microstructure and therefore inferences about physical properties;

• Development of texture and microstructure related to geological history of rock;

• Field geology and laboratory studies allow to estimate the microstucture and texture expected in an area.

Microstructure, texture and geological evolution

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tracce dei profilia

foliazione D1

SW

SW

NE

NE

direzione di trasporto D1direzione di trasporto D2

C

V

cataclasiti

!!

N

Carrara

Massa

Arni

Vinca

M. Sumbra

Pietrasanta

Unità di Massa

Complesso metamorfico delle Alpi Apuane

Basamento paleozoico

dolomia (Trias)

marmi e marmidolomitici (Lias)

calcari selciferi, diaspri, scisti sericitici,“pseudomacigno” (Dogger-Oligocene)

“Autoctono” Auct.

C

TV

A

C : Sinclinale di CarraraV : Anticlinale di VincaA : Sinclinale di M. AltissimoT : Anticlinale di M.Tambura

T

Stazzema

Vagli

Roma

Pisa

Genova

5 km0

a

b

c

d

m 0

anticlinali esinclinali D1antiformi D2

Depositi quaternari

Unità liguri e Falda Toscana

e

0 m

A

V T

1000

cb

a

d

e

500

m 0

500

m 0

Carrara marble,Alpi Apuane, Italian Northern Apennines

•Alpi Apuane tectonic window

•Jurassic limestones: marbles

•greenschists facies metamorphism during Tertiary

Microstructure, texture and geological evolution

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1) subduction, main thrusting, folding 2) metamorphism

3) later thrusting4) extension, exhumation, normal faulting

Conclusions

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• marbles usually are NOT homogeneous rocks;• marbles are thermally sensitive rocks because calcite

anisotropic behaviour, damages at low temperature;• studies on microstructures and textures in marbles

are performed at thin section scale (or even at smaller scale)

• regional and field geology investigations important to link microstructures with tectonic features in the field;

• investigating microstructure and texture in rocks is an appropriate tool for:‣better set recovery and preservations of marble

artifacts;‣ inferences about marble behaviour;‣evaluation of marble quality.

... evaluation of marble quality ...

• Amoco Corporation Building, Chicago, USA• Bowing of external marble panels: replacement

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w w w. g e o t e c n o l o g i e . u n i s i . i t / c o n t i

Slides, handouts, papers:

cont i@unis i . i t