Quantitative characterisation of mollusc shell textures D. Chateigner Lab. Physique de l’Etat Condensé (Le Mans, France) C. Hedegaard Inst. Biology, Dept. Ecology & Genetics (Aarhus, Denmark) H.-R. Wenk Dept. Geology & Geophysics (Berkeley, CA-USA)
Summary • Reference frames and experiments • Typical results with x-rays and electrons • c - and a -axes texture patterns • Twinning in nacre • Texture terms and nomenclature • Microstructure versus texture • Interest in phylogeny: example of nacre
Reference frame • Crystal: CaCO 3 , aragonite (Pmcn) or calcite (R c) 3 M • Sample: triclinic (WIMV) . G . G N M N
X-rays experiments v Point detector : λ Fe K , 4 Huber circles (DGG Berkeley) α ➱ 4 pole figures, overlaps refined in OD Arag: {111/021} + {012/121} + {102/200} + {221} Calc: {012} + {104/006} + {110} + {113} v INEL CPS 120 : λ Cu K , 4 Huber circles, (LPEC Le Mans) α ➱ 8 or 9 pole figures, partial deconvolution of overlaps Arag: … + {112/031} + {202/041} + {132/212} + {113/023} Calc: … + {202} + {024/018/116} + {211/122/1010} + {125} + {300/0012}
EBSD experiments Leo microscope + Berkeley system (DGG Berkeley) ➱ Only smoothest, large grained calcite and aragonite layers Crassostrea gigas Pteria penguin IFC ISN
Typical x-ray diffraction pattern Mytilus edulis (common mussel): sum diagrams 600000 inner sheet nacre 121/012 500000 400000 112/022/031 113/141 Intensity 300000 231/023 002 200 130 200000 041/202 132 100000 0 25 30 35 40 45 50 55 60 2 θ °
outer foliated calcite 400000 202 300000 Intensity 122/10 10 124/208/119 113 200000 104 110 018/024 300 116 121 100000 215 0 25 30 35 40 45 50 55 60 65 70 2 θ °
Microstructure versus texture Inner sheet nacre of Anodonta cygnea (river mussel) 100 010 64 1 001 0 20 µ m N a, - 45 ISN ∗ ⊥ 25 G
Microstructure versus texture Bathymodiolus thermophilus (-2400m deep mussel) 100 001 27.3 c, 0 , 90 OFC ∠ Ι 10 µ m 1 N 001 83.6 100 1 a, 90 ISN ∗ G ⊥ 38
Microstructure versus texture Euglandina sp. 001 100 a, 75 ORCL I ⊥ 22.7 100 µ m 1 001 100 N >100 a, 80 ICCL I 1 ⊥ G
Microstructure versus texture Cyclophorus woodianus 20 µ m 100 001 >100 100 µ m 1 N a, 20 IRCL I ⊥ G
OD-reliability (x-rays: point detector): Helix pomatia (Burgundy land snail: Outer com. crossed lamellar) 22.7 RP 0.05 = 67% RP 1 = 40% Lin. scale Eq. area 1 m.r.d. S = - 4.1 The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location. F 2 = 106 m.r.d. 2 OD max = 444 m.r.d.
OD-reliability (x-rays: PSD): Bathymodiolus thermophilus (deep ocean mussel: Inner sheet nacre) 31.9 RP 0.05 = 65% RP 1 = 21% 1 m.r.d. S = - 2.9 Lin. scale F 2 = 65 m.r.d. 2 Eq. area proj. OD max = 347 m.r.d.
EBSD versus X-rays: Crassostrea gigas (common oyster: Inner foliated calcite) max 1 0 2604 measured RP 0.05 = 45% 700 non-rejected x-rays: RP 1 = 31% max = 84.7 m.r.d. max = >100 m.r.d.
c -axes texture patterns Nerita Fragum Cypraea Pinctada polita fragum testudinaria maxima ICCL ICCL ICCL ISN “polished “cockle” “turtle “gold pearl nerite” cowry” oyster” ⊥ ∠ ∀ ∨
a -axes texture patterns Tectus Conus Nautilus Helix niloticus leopardus pompilius pomatia ICN ICCL ICN OCCL “commercial “leopard “new caledonia “burgundy top shell” cone” nautilus” land snail” * r | £
Twinning in aragonite ... α (110) Domain II Domain I a b α = 2 arctan(a/b) = 63.8°
… forms nacre platelets ... 1 1 ( 10) (110) ( 10) (110) ? ? Bragg, 1937 Mutvei, 1980
… that rearrange ... >100 The linked image cannot be displayed. The file may have been moved, renamed, or 16 deleted. Verify that the link points to the correct file and location. 1 1 Pinctada margaritifera Haliotis cracherodi (black pearl oyster) (black abalone)
Texture terms hkl , β c : . , ∀ , ∨ , ∠ , ⊥ c L a G α + β T a : . , £ , * , r , | a α c b N M L : ISN, ICN, ICCL T: % twinned volume <hkl>: direction in ( G , M )
Phylogenic interest: nacre = ancestral (Carter & Clarck, 1985) 21 nacre events
nacre not ancestral 9 nacre events
Conclusions • Texture analysis of shells may be quantitatively operated, with x-rays and electrons • Shells exhibit a large variety of texture patterns, from random to single crystal-like • Textural parameters are similar for close species, different for distant species • These parameters can be summarised by a “texture term” useful for species comparison • “Texture” characters can be relevant for classification and phylogenetic interpretation through cladistic analysis
Acknowledgement - University of California Museum of Paleontology, Berkeley - MARVEL expedition (1997) (Resp. Daniel Desbruyeres) Lab. d'ecologie abyssale, dept. environnement profond IFREMER Brest - HOPE expedition (1999) (Resp. Francois Lallier) Observatoire oceanologique de Roscoff Station Biologique Roscoff - Lab. Biol. Génétique Evolutive (M. Laulier, F. Denis) Univ. du Maine, Le Mans
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