Terminological Debate in the Upper Hunter Valley: Indurated Mudstone versus Tuff

Archaeologists have variously used the terms 'indurated mudstone' and 'tuff' as a description for the fine-textured, very hard, yellowish, orange, reddish-brown or grey rocks from the upper Hunter Valley from which many of the stone artefacts there were made. The desire of archaeologists working in the region to offer a precise and accurate geological description of this material has fuelled debate about whether 'tuff' or 'mudstone' is the most appropriate label. Some of the samples of these problematic rocks that we have examined petrograhically are definitely not tuff. Until much more is known about the range of lithologies represented in this group of rocks, and ways are developed to distinguish between them, the term 'IMT' ('indurated mudstone/tuff') is an acceptable alternative to the term 'mudstone' as a description for these fine-grained rocks.