Electrical conduction in olivine

Abstract

This paper reports detailed measurements of electrical conductivity σ and thermoelectric effect S in the mineral olivine and in synthetic forsterite as functions of temperature in the range from 1000° to 1500°C and oxygen partial pressure in the range from 10−10 to 104 Pa. The two most striking observations are strong conductivity anisotropy in forsterite and a sign change in S in olivine at 1390°C. These results are interpreted to show that both materials have mixed ionic and extrinsic electronic conduction under these conditions. On the basis of these interpretations, we infer that forsterite conductivity is dominated by electronic conduction in the a and b directions and probably by movement involving magnesium vacancies in the c direction, where far higher, PO2‐independent conductivity is observed. Olivine appears to show mixed conduction under all the circumstances observed; at low temperatures, electron holes dominate but are superseded by magnesium vacancies at high temperatures.

Laboratory‐based electrical conductivity in the Earth's mantle

“…For the conductivity measurements used here, olivine fO_,_ as determined by the Mo-MoO2 buffer is close to the reduction boundary of olivine and might be as much as 3 orders of magnitude lower than that of the upper mantle. Olivine could vary by as much as./'•) 2 to the 1/6 power although its fi32 dependence is lower at lower jO2 [Schock et al, 1989;Duba and Constable, 1993]. Hence o!ivine conductivity at oxygen fugacity close to FMQ could be as much as ,--0.5 log unit higher (an upper limit) than that buffered by using a Mo-MoO2 buffer.…”

Electrical conductivity of synthetic iron-bearing olivine

“…Figure 4b shows that conductivity in a single crystal along a particular crystallographic axis is higher than for aggregates (Constable and Duba 1990;Roberts and Tyburczy 1993a), illustrating the blocking nature of the grain boundaries present in the aggregate at lower fO 2 . Also it appears that the difference between the Red Sea olivine (single crystal) (Schock et al 1989) and San Carlos olivine (single crystal) (Du Frane et al 2005) is almost one order of magnitude, thus highlighting the natural compositional variation and possibly more oxidized state of San Carlos material. The data from ten Grotenhuis et al (2004) show, in Fig.…”

Velocity–conductivity relationships for mantle mineral assemblages in Archean cratonic lithosphere based on a review of laboratory data and Hashin–Shtrikman extremal bounds

“…In his work, conductivity is given by the summation of two conduction mechanisms, one resulting from polarons (conducting electrons in an ionic crystal lattice) and the other from magnesium vacancies. The change in dominance of conduction mechanism between the two occurs at a temperature around 1300 °C (Schock et al, 1989), which is approximately the temperature at the base of the lithosphere. Conductivity can be thus described as Temperature can be estimated from either geothermal models or from petrological analyses of mantle xenoliths.…”

“…Decreasing Mg# by replacing magnesium by iron results in increased electrical conductivity in all minerals, especially olivine (e.g., Schock et al, 1989;Vacher and Verhoeven, 2007). This well-known effect, where iron chemically substitutes for magnesium in the dodecahedral site while maintaining a fixed lattice symmetry, has been studied in olivine and pyroxene since the early 1980s (Hinze et al, 1981;Seifert et al, 1982), and most recently in garnet by Romano et al (2006).…”