Variety of Iron Oxide Inclusions in Sapphire from Southern Vietnam: Indication of Environmental Change during Crystallization

Abstract

Sapphires from alluvial deposits associated with Cenozoic basalts in Southern Vietnam were collected for investigation of mineral inclusions. In this report, primary iron oxide inclusions were focused on, with detailed mineral chemistry using a Raman spectroscope and electron probe micro-analyzer. Consequently, a variety of iron oxide inclusions were recognized as wüstite, hercynite, and ilmenite. Ilmenite falling within an ilmenite–hematite series ranged in composition between Il24-30He36-38Mt35-40 and Il49-54He34-40Mt7-10, classified as titanomagnetite and titanohematite, respectively. Wüstite with non-stoichiometry, (Fe2+0.3-0.9)(Ti3+<0.179Al3+≤0.6Cr3+<0.1Fe3+≤0.46)☐≤0.23O, was associated with hercynite inclusions, clearly indicating cogenetic sapphire formation. Wüstite and sapphire appear to have been formed from the breakdown reaction of hercynite (hercynite = sapphire+wüstite) within a reduction magma chamber. Titanohematite and titanomagnetite series might have crystallized during iron–titanium reequilibration via subsolidus exsolution under a slightly oxidized cooling process.

Archaeometallurgical Characterization of Two Lombard Early Medieval Bloomery Slags from Ponte di Val Gabbia I Site (Northern Italy)

“…In fact, and 385 cm −1 match with hematite (Figure 5b) [40]. However, these due to the laser-induced oxidation of wüstite to hematite [40][41][42]. O Raman peak at 585 cm −1 can be assigned to wüstite or hematite (Fi presence of leucite in slag A was proven by the Raman peak locate 5c) [44][45][46].…”

“…In fact, the lines at 215, 273, −1 match with hematite (Figure 5b) [40]. However, these bands are probably laser-induced oxidation of wüstite to hematite [40][41][42]. On the other hand, the ak at 585 cm −1 can be assigned to wüstite or hematite (Figure 5b) [42,43].…”

“…The oxidation effect caused by the laser prevented a proper characterization of the outer iron oxide skin of slag B. In fact, the hematite peaks at 212, 275, and 387 cm −1 are probably due to the oxidation of wüstite and/or magnetite [40][41][42] (Figure 6c). In addition, the interpretation of the peak positioned at 595 cm −1 is rather controversial because it can be attributed to both wüstite and hematite (Figure 6c) [40,47].…”