Quarry Void

The quarry void at Hornsby Quarry is not a subtle thing. Rock faces rise on all sides, near-vertical and dark, cut through a body of volcanic dolerite that formed between 146 and 200 million years ago. Still water sits at the floor of the void, catching the faint light that reaches down from above. At its deepest point, the southern face drops approximately 120 metres. The void spans roughly 300 metres across. The photograph was made in 2015, when the site had been quiet for more than a decade. The quarry sits within the Hornsby diatreme, a large oval volcanic neck located in Old Mans Valley, off Quarry Road, Hornsby. The diatreme is the largest of its kind in the Sydney area and one of the best-preserved of approximately 150 mafic diatremes recorded within the Sydney Basin. Quarrying began around 1905, when the Higgins family started extracting dolerite from the site. Hornsby Shire Council purchased the operation in 1912, recognising the dolerite as essential material for constructing and maintaining local roads across northern Sydney. Ownership changed hands several times across the following decades, passing through Hornsby Blue Metal Limited, then Farley and Lewers from 1959, then CSR Construction Materials from 1981. Quarrying ceased in 2002. Hornsby Shire Council acquired the site in 2003 after a price of $26,508,771.28 was determined by the NSW Land and Environment Court. In 2022, geologist Ian G. Percival published an assessment classifying the quarry as an internationally significant geological reference site, recognising the eastern quarry face as an outstanding cross-section through the volcanic neck. What the photograph records is that same exposed geology: dark dolerite walls, the accumulated water below, and the open sky reflected back up from the floor of a void that took nearly a century of extraction to create.