Erionite is a naturally-occurring zeolite mineral series with a fibrous-asbestiform shape, that has been linked to malignant mesothelioma due to its high biopersistence and respirability. Despite its potential health risks, its occurrence, variability and environmental significance in New Zealand remain poorly understood. This study aims to better understand the occurrence of erionite by investigating its geological settings, crystal chemistry, and morphological variability. A total of 138 samples were initially screened for erionite occurrence, from which three localities were selected for detailed characterisation: Kaipara, Auckland, and Mount Somers, representing erionite-Na, erionite-Ca and erionite-K, respectively. A comprehensive stepwise analytical approach was employed, initially using PXRD and SEM-EDS for phase identification and morphological analysis. Where erionite was identified, further analysis was conducted using TEM-3DED, micro-Raman and EMPA. Results reveal that palaeoenvironmental conditions influence erionite’s crystal habits and composition, occurring as prismatic aggregates, acicular bundles and woolly asbestiform fibres. Many of the fibres met the World Health Organization (WHO) respirability criteria, highlighting potential health risks if airborne. Although bulk concentrations are relatively low, the presence of respirable fibres in both rural and urban settings raises concerns regarding potential environmental exposure during earthworks and construction. This study establishes the link between erionite’s geological setting and morphology. Providing essential data to inform environmental monitoring, land-use planning and risk mitigation in areas where erionite-bearing rocks may be disturbed.