A possible origin of malachite’s distinctive banding

Malachite – a vibrant green mineral – is widely used to make jewellery and decorative items but for all the millennia it has been known, no one has explained its perfect geometric banding. In a new paper, published by American Mineralogist on 2nd April 2020, Dr Dominic Papineau (UCL Earth Sciences and The Centre for Planetary Sciences at UCL/Birckbeck) explains that oscillating chemical reactions could be responsible for the banding because these have comparable geometric patterns and chemical composition to the bands formed using the classical reactants of the Belousov-Zhabotinsky (B-Z) reaction.

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Links

Research paper in American Minerogolist
Publically accessible preprint from the Mineralogical Society of America
Dr Dominic Papineau's academic profile
UCL Department of Earth Sciences
 

Image

Morphological comparison of sub-millimetric to decimetric self-similar patterns in chemically oscillating experiments (left, orange-blue coloured liquid in 1 dm diameter Petri dish) and in botryoidal malachite (right, specimen from private collection). Credit: D. Papineau (UCL).

Video

Chemically-oscillating experiment, in a 10 centimetre diameter Petri dish on a LED light board, with orange ferroin redox indicator and the reactants of the classical Belousov-Zhabotinsky reaction. The grey-blue circular chemical waves are seen to diffuse away from randomly located oxidation spots over minutes times scales. Note that the destructive interference of the circular waves leads to the trace being erased when they meet, which is also a characteristic feature of botryoidal malachite.

Created by D. Papineau (UCL), edited by M. Chalmers (UCL).
Music credit: Rachmaninov Piano Concerto No. 3, Sinfonia of Leeds 2004 (Creative Commons - imsip.org).

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Bex Caygill

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Email: r.caygill [at] ucl.ac.uk