Reply 2 to comment on “Ultra-high pressure and ultra-reduced minerals in ophiolites may form by lightning strikes”

We appreciate the comments by Yang et al. (2018) to our recent proposal (Ballhaus et al., 2017) that high pressure and ultra-reduced minerals in ophiolites may form by lightning strikes. We have carried out additional experiments to address the issues raised by Yang et al. (2018). We maintain that the ultra-reduced phases in ophiolites are best explained as plasma precipitates generated by lightning strikes. Yang et al. (2018) note that ultra-reduced phases are recovered from chromitite ore sampled tens of meters below the surface. Previously, no information was provided regarding the recovery depth of phases like SiC, presumably because a near-surface origin was not considered. To semi-quantify the penetration depth of lightning bolts in crystalline rocks we measured the specific resistances of various lithologies (Fig. 1a). We note that chromitites are more conductive by ~2 orders of magnitude than silicate rocks. A rock body with a higher conductivity can provide a guide path for cloud-toground discharges more effectively than a lithology with lower conductivity, as cloud-to-ground discharges need a counter-pole capable of accumulating charges. The “semi-conductive” nature of the rock allows the buildup of a high electrical field which is imperative for the formation of a plasma. The penetration depth of a lightning strike is probably determined by many factors; electrical conductivity and the 3D orientation of the target rock, faulting/fracturing, presence or not of H2O along grain boundaries and fractures. We put to the discussion the possibility that conductive lithologies like chromitite exposed to frequent lightning may accumulate over time appreciable quantities of lightning strike minerals.