Microstructures, textures and material properties of marble rocks
Paolo Conti
, Italy
Samos Training School, 26-30 August 2013 Contents
• Marble behaviour • Crystal structure of minerals and rocks • Rock fabrics • Marble deterioration • Mechanical properties • Natural examples
2 Marbles: different behaviour
(Ephesus, Turkey) (from Shushakova et al., 2010) 3 Marbles: different behaviour
panels
4 Marbles: different behaviour
5 Marbles
Same composition (≃100 % CaCO3)
Different behaviour due to: • anisotropic physical properties of calcite crystals • texture of rocks • microstructure of rocks
6 Anisotropic physical properties: Crystal structure of rocks
7 Anisotropic physical properties: strength crystal “weak” bond
“strong” bond
8 Anisotropic physical properties: strength crystal “weak” bond
“strong” bond
9 Anisotropic physical properties: thermal expansion Increasing temperature: stretch of bond length “weak” bond
“strong” bond
10 Anisotropic physical properties: thermal expansion
(Winkler, 1994)
11 Anisotropic physical properties: natural texture
crystallographic direction
weak strong crystallographic crystallographic preferred preferred orientation orientation
(a) (b) (c) (d) (e) 12 Anisotropic physical properties: shapes
(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
13 Anisotropic physical properties: shapes
straight grain lobate grain boundaries boundaries “slide” “locked”
14 Anisotropic physical properties: shapes
no shape preferred shape preferred orientation of crystals orientation of crystals
(anisotropic volume increase)
15 Developement of microstructures (movies)
dynamic before: no shape preferred (syn-tectonic) orientation, straight recrystallization grain boundaries
static before: recrystallization shape preferred orientation, lobate (annealing) grain boundaries
Octachloropropane (organic material) http://www.atmos.albany.edu/geology/ Means et al. (1994) J. Struct. Geol.,16, 403-418 webpages/wdmovies/wdmoviep.html 16 Anisotropic physical properties
(a) (b) (c) (d) (e) •no shape preferred •no shape preferred •shape preferred •shape preferred orientation of orientation of orientation of orientation of grains grains grains grains •no crystallographic •crystallographic •no crystallographic •crystallographic preferred preferred preferred preferred orientation orientation orientation orientation
crystallographic preferred orientation of crystals = texture of rock shape preferred orientation of crystals = microstructure of rock
(texture + microstructure = fabric)
17 In marbles...
limited informations from outcrop studies only
18 Microstructures in marbles “ultra” thin section (<8 µm)
19 Microstructures in marbles
Carrara marble (Italy)
(Carmignani, Conti, et al., 2007)
20 Microstructures in marbles: measure
(Molli, Conti et al., 2007)
21 Textures in marbles: measure
(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.)
22 In marble rocks ...
• 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.
23 Microstructure, texture and geological evolution
Genova
Pisa
Roma
Carrara marble, Vinca L Alpi Apuane, Italian a d V Vagli b T
Northern Apennines c C
A Carrara
M. Sumbra
Arni
T Alpi Apuane tectonic Massa • C : Sinclinale di Carrara V : Anticlinale di Vinca A : Sinclinale di M. Altissimo window T : Anticlinale di M.Tambura Depositi quaternari e
Unità liguri e Falda Toscana Stazzema
Complesso metamorfico delle Alpi Apuane •Jurassic limestones: Unità di Massa Autoctono Auct. calcari selciferi, diaspri, scisti sericitici, pseudomacigno (Dogger-Oligocene)
marbles marmi e marmi foliazione D1 dolomitici (Lias) Pietrasanta anticlinali e N dolomia (Trias) sinclinali D1 antiformi D2 Basamento paleozoico 0 5 km a tracce dei profili •greenschists facies direzione di trasporto D1 SW direzione di trasporto D2
metamorphism during m 0 a NE C
0 m 500 1000 Tertiary b m 0 V c A d cataclasiti V T
SW NE 500
m 0
e 24 Microstructure, texture and geological evolution 1) subduction, main thrusting, folding 2) metamorphism
3) later thrusting 4) extension, exhumation, normal faulting 25 Conclusions
• 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.
26 ... evaluation of marble quality ...
• Amoco Corporation Building, Chicago, USA • Bowing of external marble panels: replacement
27 Slides, handouts, papers: www.geotecnologie.unisi.it/conti
28