Visualisation and quantification of CV chondrite petrography using micro-tomography Dominik C. Hezel a,⇑ , Premkumar Elangovan a,1 , Sebastian Viehmann b , Lauren Howard a , Richard L. Abel a,2 , Robin Armstrong a a Natural History Museum, Department of Mineralogy, Cromwell Road, SW7 5BD London, UK b Jacobs University Bremen, School of Engineering and Science, Campus Ring 1, 28759 Bremen, Germany Available online 24 March 2012 Abstract Micro-computed tomography is a non-destructive technique that allows the study of 3D meteorite petrography. The tech- nique produces a unique and instructive visualisation of the meteorite for quantifying its components. We studied the overall petrography of the two CV chondrites Allende and Mokoia to constrain their formation histories. A set of movies and ste- reographic images detail the 3D petrography. Component modal abundances agree with previous reports and modal abun- dance differences between Allende and Mokoia support the chondrule–matrix complementarity and that chondrules and matrix formed from the same chemical reservoir. We identified two types of chondrules, a normal type and one where a nor- mal type I or II chondrule is almost completely encapsulated by an opaque-rich layer. This layer was probably acquired dur- ing a late stage condensation process. The appearance of opaques in chondrules and matrix is different, not supporting a genetic relationships between these. Low abundances of compound chondrules (1.75 vol% in Allende and 2.50 vol% in Mokoia) indicate low chondrule densities and/or low relative component velocities in chondrule formation regions. Porosities on a scale <10–20 lm allowed for only local aqueous alteration processes on the meteorite parent bodies. Ó 2012 Elsevier Ltd. All rights reserved. 1. INTRODUCTION Petrographic knowledge of meteorites is required to address a range of important problems in meteoritics. For example, component modal abundances are needed to evaluate their compositional relationship. More detailed abundances such as the occurrence of opaques in chond- rules and matrix sets constraints on the formation of the opaques. The density of chondrule formation regions can be inferred from the number of compound chondrules. The agglomeration of meteorite parent bodies can be in part deduced from the texture and distribution of compo- nents. Meteorite porosity pertains to discuss permeabilities and the likelihood of aqueous alteration. Component porosities might provide an insight to the nature of their precursors whilst cracks record, e.g. shock events. So far, meteorite petrography has been studied using 2D sections. The disadvantages of this approach are (i) the true 3D petrography is insufficiently represented (e.g. Chayes, 1956; Underwood, 1970; Eisenhour, 1996; Hezel, 2007; Friedrich, 2008; Ebel et al., 2008), (ii) a comparatively small part of the meteorite is studied (Hezel et al., 2008) and (iii) the meteorite needs to be destroyed to prepare the section. The advantage of this technique is that the section can be studied in great detail. Computer aided micro-tomography (l-CT) resolves many of the shortcomings of studying 2D sections. It facil- itates the study of true 3D meteorite petrography. Hence, its advantages are (i) true 3D petrography of the meteorite, (ii) small (several tens of lm 3 ) as well as large (several 0016-7037/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.gca.2012.03.015 ⇑ Corresponding author. Present address: University of Cologne, Department of Geology and Mineralogy, Zu ¨ lpicher Str. 49b, 50674 Ko ¨ ln, Germany. E-mail address: dominik.hezel@uni-koeln.de (D.C. Hezel). 1 Present address: CVSSP, University of Surrey, Department of Electronic Engineering, Guildford, GU2 7XH Surrey, UK. 2 Present address: Department of Surgery and Cancer, Faculty of Medicine, Imperial College, Charing Cross Hospital, W6 8RP London, UK. www.elsevier.com/locate/gca Available online at www.sciencedirect.com Geochimica et Cosmochimica Acta 116 (2013) 33–40