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Investigation of microstructural anisotropy of limestone

Ladislav Kalvoda 1Maja Dlouhá 1Martin Dráb 1Jan Drahokoupil 1Alexander Grishin 1Jiri Marek 1Petr Sedlak 2Stanislav Vratislav 1Jindrich Hladil 3Martin Chadima 3Winfried Kockelmann 4

1. Czech Technical University in Prague, The Faculty of Nuclear Sciences and Physical Engineering, Trojanova 13, Prague 2, Prague 12000, Czech Republic
2. Institute of Thermomechanics v.v.i., Academy of Sciences of the Czech Republic, Dolejskova 5, Prague 12000, Czech Republic
3. Czech Academy of Sciences, Institute of geology (IG), Rozvojová 269, Prague 16500, Czech Republic
4. Science and technology facilities council, Rutherford Appleton laboratory, Didcot OX110QX, United Kingdom


Composition, crystalline structure and microstructural anisotropy of limestone is investigated by means of instrumental neutron activation analysis (INAA), X-ray diffraction (XRD), neutron diffraction (ND) and measurement of anisotropy of magnetic susceptibility (AMS) and anisotropy of resonant ultrasound spectroscopy (ARUS).
The samples were collected near Choteč, Bohemia (Na Škrábku quarry, SE corner; 49°59'19.57" N, 14°16'44.16" E), from a single overturned/recumbent fold. Elementary composition of the investigated limestone (INAA) is dominated by Ca (34.72 mass %), Mg (4733 ppm), Fe (2253 ppm), K (1967 ppm) and Al (1185 ppm). In addition, traces of another 33 elements are present having concentration higher then 1 ppm. Total organic carbon (TOC) concentration is only ~0.15 mass %. Calcite (~ 98.5+-1 mass %) and quartz (~ 1.5+-1 mass %) were identified by phase analysis of XRD powder patterns as the prevailing mineral phases. Based on ND powder data, crystalline structure of calcite was refined within the space group R-3c giving the lattice parameters a = 0.4915(4) nm and c = 1.6800(14) nm.
Crystallographic preferential orientation (CPO) of the crystalline calcite cement filling the initial sediment pores is weak (XRD and ND data). Obtained ARUS patterns exhibit sharp resonances approving the complete pore filling. The calculated sharpness (f) of the orientation distribution functions (ODF) calculated for individual samples was f < 3. The observed mean polar angle (Beta) between the c-poles and the original sedimentation direction (SD) varies with the point of sample collection within the broad range: Beta = 0o - 60o. Orientation of (110) poles around the <0001> direction is practically isotropic.
Small positive values of the mean magnetic susceptibility (χ) were obtained by KLY-2 bridge measurement): χ = 3 - 8 x 10-9 m3 kg-1. It is apparent that the intrinsic diamagnetic contribution of calcite is balanced by an extrinsic para-/ferro-magnetic contribution. Noisy AMS results caused only the direction of the pole to the magnetic foliation (MF) could be identified. The observed mean MF deflection from SD varies in accord with the textural Beta-value.

This research has been supported by grants MSM6840770040, AV0Z30130516 and GACR205/08/0767.


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Related papers

Presentation: Poster at 11th European Powder Diffraction Conference, Poster session, by Ladislav Kalvoda
See On-line Journal of 11th European Powder Diffraction Conference

Submitted: 2008-04-30 17:41
Revised:   2009-06-07 00:48