Fig. 5
From: Weathering in a world without terrestrial life recorded in the Mesoproterozoic Velkerri Formation
SEM backscatter images overlain by a Nanomin mineral map illustrating mineral replacement by kaolinite and illite. a Only kaolinite selected in the mineral map layer overlay showing euhedral kaolinite crystals formed within a 40 µm void most likely formed by feldspar dissolution (from the Urapunga-4 core). b albite, pyrite, and kaolinite selected in the mineral map overlay showing partial dissolution of a 20 µm feldspar crystal with authigenic kaolinite forming within the mouldic porosity. The boundaries of the minerals identified by Nanomin mineral mapping and the characteristic shapes of the minerals evident in BSE provide qualitative sense of the precision and accuracy mineral assignments (from the Walton-2 core). c A 70 µm biotite flake with alteration of the ends to kaolinite and illite. Illite replacement of smaller detrital mica minerals including a fan of small 2–4 µm crystals forming a floccule squeezed between the two large mica flakes. Detrital quartz grains sutured together by quartz overgrowth, and detrital rutile also evident. Dashed yellow line outlines an area of secondary porosity formed by feldspar dissolution with hairy, authigenic illite/smectite forming within it (from the Lady Penhryn-2 core). Scale bar = 10 μm
