The pedogenesis of an acid sulfate soil incorporates the development of oxidised clay material from unoxidised gel material. Despite the fact that the overall oxidation processes within these sediments have been widely researched – little is known about the micro-scale interactions of the sulfidic, generally clayey, sediments and their oxidation products.

The idealised pedogenic model of acid sulfate soil development involves the collapse of the ‘house of cards’ structure that exists within the gel material. The unoxidised gel sediments can contain up to 80% water in both superficial and structural forms which is irreversibly lost upon oxidation. The phenomenon of the ‘house of cards’ collapse should result in clay platelets forming ‘face to face’ bonds rather than ‘edge to face’ bonds.

The physical verification of this ‘house of cards’ structure - although theoretically well established - has eluded scientific research due to artefacts created within sampling and within analytical methodologies. Detailed structural analysis of these acid sulfate materials has been undertaken and will be presented. Techniques including; scanning electron microscopy, transmission electron microscopy and X-ray diffraction will be discussed.

This paper assesses the viability and applicability of the ‘house of cards’ structures to unoxidised sulfidic clay sediments and the subsequent collapse of these structures post-oxidation. The verification of these structures provides great insight into sediment formation over time and builds upon the pedogenic model for acid sulfate soil development first proposed over 20 years ago.