Tales of the unexpected: halloysite delivers surprises and a paradox

Abstract

Despite being first described nearly 200 years ago, halloysite still has the capacity to surprise. We report here the remarkable discovery in New Zealand of two new morphologies for this 1:1 Si:Al layered aluminosilicate member of the kaolin subgroup. One discovery was entirely serendipitous, thus lending validity to the famous phrase attributed to scientist Isaac Asimov: The most exciting phrase to hear in science, the one that heralds new discoveries, is not “Eureka” but “That’s funny...”. Moreover, the recognition of one of the new morphologies of halloysite helped enable a long-standing problem regarding the geotechnical property of sensitivity and its impact on landsliding in the Tauranga region, eastern North Island, to be solved. Such landsliding has commonly been attributed (possibly erroneously) to the dominance of nanocrystalline allophane, the clay commonly associated with halloysite in many weathered pyroclastic sequences and volcanogenic soils in North Island. In this article, we briefly summarise the circumstances and implications of the two discoveries relating to halloysite morphology, one published in Clay Minerals and the other in Geology, and a third study (also in Clay Minerals) relating in part to the formation of halloysite.