Investigation of olivine's thermostability in an oxidized and reduced atmosphere

Olivine is an abundant phase of ultramafic and mafic rocks in the earth's crust and mantle. Stony meteorites or stony-iron meteorites like pallasites also contain a lot of extraterrestrial olivines. During atmosphere entry olivine-containing meteorites experience different oxygen levels and intense heating for brief intervals, creating fusion crusts that are a few millimetres thick. As a result, various thermal pathways between the rim and the core are anticipated for meteoritic olivines. This shows different colours in natural pallasitic olivines. We are particularly interested in the effects of environmental variables on both terrestrial and interplanetary olivines, based on terrestrial olivines. Natural volcanic olivines from the 1959 Kilauea eruption in Hawaii, the Aheim mine, Norway, are employed and a stony-iron pallasite (collected 1822 – Atacama Desert). We generate two environments using a gas-tight tube furnace that produces CO-CO2 gas mixes—one in air and the second with a reduced atmosphere (fO₂10^-12 bar). The temperatures range from 950 to 1350 degrees Celsius (i.e. within the olivine stability field). After hand-picking single grains of olivines and putting them in Pt-Rh crucibles for an hour, the samples are lifted vertically out of the tube furnace and quenched in air. EPMA, SEM, RAMAN, and optical and laser microscopy are used to characterise and analyse the samples.

Preliminary findings, olivines show thermal stability and have a homogeneous chemical composition both before and after heating. A reduced environmental exposure causes a change in colour, similar to the stony-iron pallasite which will be discussed. In association with those observations, we also see Raman bands nearby 600 cm-1 vanish, and Raman bands show up at 800 cm-1. We will compare these effects in relation to the findings from tests involving air exposure and compare the observations obtained from naturally occurring pallasitic olivines.