Revisiting the felsőbányaite-basaluminite question : nomenclatural synonymy and unresolved structural issues

Olivier Pourret , Haiyan Liu

Felsőbányaite (1853) and basaluminite (1948) share the formula Al4(SO4)(OH)10·4H2O, and were shown to be crystallographically identical in 1997, leading the IMA to discredit basaluminite in 2006 in favor of the older name. This nomenclatural choice is not an issue. Instead, this opinion article explores a more focused contemporary question: is the poorly crystalline material that geochemists continue to refer to as basaluminite in acid mine drainage (AMD) and acid sulfate soil (ASS) the same as the well-ordered felsőbányaite of the type locality at all structural scales? In addition to nanoscale point flaws, XRD/PDF and EXAFS study has revealed a pattern in which the two materials do not co-occur as a single species undergoing gradual ordering usually would. Rather than seeking to overturn the 2006 verdict, some researchers have acknowledged the similarity between the two materials as possibly “fortuitous”. The evidence basis is actual but limited, primarily based on work by a single research group. 97.6% of applied AMD/ASS articles employing either term as a working identification still use basaluminite, according to a full-text literature count (using Dimensions.ai, 2006–2025), which shows that the applied literature has, in practice, not adopted the ruling after articles using both names in passing are set aside. In order to resolve the issue, the present study compares the strength of the original crystallographic case with the structural evidence, outlines what kind of findings would and would not elevate the distinction to species status, and suggests a direct comparative study along with more explicit reporting practices in the applied literature.