High-coercivity magnetic minerals in archaeological baked clay and bricks
Document Type
Article
Publication Date
10-23-2020
Department
Department of Geological and Mining Engineering and Sciences
Abstract
The thorough understanding of magnetic mineralogy is a prerequisite of any successful palaeomagnetic or archaeomagnetic study. Magnetic minerals in archaeological ceramics and baked clay may be inherited from the parent material or, more frequently, formed during the firing process. The resulting magnetic mineralogy may be complex, including ferrimagnetic phases not commonly encountered in rocks. Towards this end, we carried out a detailed rock magnetic study on a representative collection of archaeological ceramics (baked clay from combustion structures and bricks) from Bulgaria and Russia. Experiments included measurement of isothermal remanence acquisition and demagnetization as a function of temperature between 20 and >600 °C. For selected samples, low-temperature measurements of saturation remanence and initial magnetic susceptibility between 1.8 and 300 K have been carried out. All studied samples contain a magnetically soft mineral identified as maghemite probably substituted by Ti, Mn and/or Al. Stoichiometric magnetite has never been observed, as evidenced by the absence of the Verwey phase transition. In addition, one or two magnetically hard mineral phases have been detected, differing sharply in their respective unblocking temperatures. One of these unblocking between 540 and 620 °C is believed to be substituted hematite. Another phase unblocks at much lower temperatures, between 140 and 240 °C, and its magnetic properties correspond to an enigmatic high coercivity, stable, low-unblocking temperature (HCSLT) phase reported earlier. In a few samples, high-and low unblocking temperature, magnetically hard phases appear to coexist; in the others, the HCSLT phase is the only magnetically hard mineral present.
Publication Title
Geophysical Journal International
Recommended Citation
Kosterov, A.,
Kovacheva, M.,
Kostadinova-Avramova, M.,
Minaev, P.,
Salnaia, N.,
Surovitskii, L.,
Yanson, S.,
Sergienko, E.,
&
Kharitonskii, P.
(2020).
High-coercivity magnetic minerals in archaeological baked clay and bricks.
Geophysical Journal International,
224(2), 1256-1271.
http://doi.org/10.1093/gji/ggaa508
Retrieved from: https://digitalcommons.mtu.edu/michigantech-p/14605
Publisher's Statement
© 2021 The Author(s). Published by Oxford University Press on behalf of The Royal Astronomical Society. Publisher’s version of record: https://doi.org/10.1093/gji/ggaa508