The Hornsby Quarry Geosite, NSW, Australia—A Geoheritage Treasure

Quarrying for aggregate material at Hornsby in New South Wales (Australia) exposed a >100 m-deep cross-section of the volcanic neck Jurassic diatreme, which extruded through Sydney Basin deposits. The reveals features many scales. Globally, there are very few instances such excellent 3D exposure. It is arguable that this exposure alone makes it geosite international value. However, evaluation Diatreme using geoheritage toolkit shows meets various conservation criteria, being reference site, and an historically culturally important as well hosting archival material. has significant scales: macroscale, where dish beds visible on all quarry walls, preserving structure formed during accretion later caldera collapse; mesoscale, breccia surge layers visible, providing insight into how magma interacted with host rock types; microscale, lapilli, chilled margins blocks, carbon-rich xenoliths hand specimens. As such, Quarry hosts world-class array preserves period post-volcanic history within Basin, fostering geoeducation geotourism.