Fig. 4: Post-VHT images of various samples.

a Coupons of BA5 amphibolite melted at 1250 °C and 1400 °C, and of laboratory oxides of similar compositions after VHT for 24 days at 200 °C and (b) corresponding BSE-SEM of a cross section of BA5 1250 °C. c Coupons of 443 Granite melted at 1250 °C and 1400 °C, and of laboratory oxides of similar compositions after VHT, for 24 days at 200 °C (d) and corresponding SEM of a cross section of 443 Granite 1400 °C.