Magnetic properties and electron spin resonance of Ecuadorian obsidians. Application to provenance research of archeological samples

Much More Than a Glass: The Complex Magnetic and Microstructural Properties of Obsidian

“…The saturation magnetization value has been found at about 0.12 emu/g (normalized for the total mass of sample), which are in agreement with the values found by other authors for obsidian samples of different provenance, among which are Sardinian ones. [22][23][24]26 The hysteretic behavior (H c (N141) = 202 ± 10 Oe; M r /M s (N141) = 0.13 ± 0.01) evidences the presence of a population of RT-blocked single-domain and/or multidomain particles that accompany the population of superparamagnetic nanoparticles, evidenced by ZFC-FC curves. At 30 K, an increase of the slope at high field and a ferromagnetic behavior with M r /M s and H c ≠ 0 is observed.…”

“…In the literature, most studies about obsidian are dedicated to the application of an analytical technique, both destructive and nondestructive, with the aim of discriminating the main sources and subsources for archeological purposes. Other studies are devoted to the characterization of the obsidian as a material − dealing with different aspects such as the color or optical properties, ,,, the glass structure, ,, the comparison of its properties with those of impact glasses , or artificial ones, , its formation process, ,, the different coordination of iron ions, − and the paleointensity studies. , Previous work has also been devoted to the study of the magnetic properties of obsidian samples of different sources worldwide by magnetometry, ,− ,− EPR, ,,, and 57 Fe Mössbauer spectroscopy, ,,,− ,, among which some refer to Sardinian obsidians. ,,,− The great majority of the authors evidenced the coexistence of paramagnetism with ferrimagnetism and/or superparamagnetism associated with magnetite nanoparticles. Some authors underlined the possibility to distinguish magnetite of different sizes from single domain to multidomain. ,,,, However, to date a comprehensive correlation of the ...…”

“…Some authors underlined the possibility to distinguish magnetite of different sizes from single domain to multidomain. ,,,, However, to date a comprehensive correlation of the magnetic properties with the microstructure and morphology of Monte Arci obsidian is still lacking, despite the evidence for the copresence of a glassy matrix together with iron-containing micro- or nanolites. Indeed, although obsidian is usually defined as a natural glass, it is known from the literature that crystalline inclusions and occlusions, − ,− among which, iron-based minerals, are often present, also in the case of the Monte Arci obsidian. ,,,,,, Feldspars (KAlSi 3 O 8 – NaAlSi 3 O 8 – CaAl 2 Si 2 O 8 ), ,,,,,,, pyroxenes (XY­(Si,Al) 2 O 6 ), ,,,, biotite (K­(Mg,Fe) 3 AlSi 3 O 10 (OH) 2 ), ,, hornblende ((Ca,Na) 2–3 (Mg,Fe,Al) 5 (Al,Si) 8 O 22 (OH,F) 2 ), ,, silica polymorphs (cristobalite, tridymite, quartz), ,, apatite (Ca 10 (PO 4 ) 6 (OH,F,Cl) 2 ), , zircon (ZrSiO 4 ), , titanomagnetite/magnetite or related spinels (Fe 3 O 4 , Fe 2+ (Fe 3+ ,Ti) 2 O 4 ), ,− ,,…”

Intra-Source Provenance Study on Monte Arci (Sardinia) Obsidian by pXRF: Role of the Data Acquisition and Analysis Tools

“…In prehistory, obsidian has been preferably exploited even in places where alternative materials were available and exchange networks have been established in time [38]. Indeed, sources of obsidian are limited in number and often located far away from the archaeological sites where the artifacts are discovered [26]. This aspect has represented the ideal premise for the archaeologists to reconstruct the routes of obsidian circulation and subsequently the social and economic organisation of the ancient communities and their interactions by means of provenance studies, based on the assignment of each artefact to the outcrop [26,39,40].…”

“…Indeed, sources of obsidian are limited in number and often located far away from the archaeological sites where the artifacts are discovered [26]. This aspect has represented the ideal premise for the archaeologists to reconstruct the routes of obsidian circulation and subsequently the social and economic organisation of the ancient communities and their interactions by means of provenance studies, based on the assignment of each artefact to the outcrop [26,39,40]. Indeed, each obsidian source has its own geological history for both thermodynamic and cooling conditions, which has produced specific chemical, physical and structural features [16].…”