TY - JOUR

T1 - High-coercivity magnetic minerals in archaeological baked clay and bricks

AU - Kosterov, Andrei

AU - Kovacheva, Mary

AU - Kostadinova-Avramova, Maria

AU - Minaev, Pavel

AU - Salnaia, Natalia

AU - Surovitskii, Leonid

AU - Yanson, Svetlana

AU - Sergienko, Elena

AU - Kharitonskii, Petr

N1 - Publisher Copyright: © 2021 The Author(s). Published by Oxford University Press on behalf of The Royal Astronomical Society.

PY - 2021/2/1

Y1 - 2021/2/1

N2 - 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.

AB - 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.

KW - Archaeomagnetism

KW - Magnetic mineralogy and petrology

KW - Magnetic properties

KW - Rock and mineral magnetism

UR - http://www.scopus.com/inward/record.url?scp=85099880540&partnerID=8YFLogxK

U2 - 10.1093/gji/ggaa508

DO - 10.1093/gji/ggaa508

M3 - Article

VL - 224

SP - 1257

EP - 1272

JO - Geophysical Journal International

JF - Geophysical Journal International

SN - 0956-540X

IS - 2

ER -