Workers at the Bundanoon Sandstone quarry in Harris Street, Pyrmont. The yellow block sandstone will be used to restore some of the city's most important heritage buildings. Credit:Louise Kennerley The State Library of NSW, the Australian Museum, the GPO building, the QVB building, just to name a few, were all hewn from Pyrmont's yellow block sandstone. Troy Stratti, managing director of Bundanoon Sandstone, the company excavating the Harris Street site, said the value of yellow block was in its link to the past. There is little commercial demand for it otherwise. "It is sought after in the sense that it is a stone needed now for heritage restoration," he said. "It's important not to look at it in commercial way. There's a social responsibility here." Human-sized saws have already sliced and diced some 2000 cubic metres of sandstone into geometrically-precise blocks.

A massive saw is used to cut the sandstone into blocks before they are extracted and transported out of the quarry. Credit:Louise Kennerley Mr Stratti is hopefully the total yield will be double this, and some 1300 blocks will be extracted before the project wraps up early next year. At that point, developers TWT developments will begin building high-end terraces on the site. Most of the stone, he said, will be used to replenish the government's dwindling yellow block supply at the government-run Ministers Stonework Program, where it will be used by stonemasons to restore the city's heritage sandstone buildings. A worker traverses the yellow block boulders at the Bundanoon Sandstone quarry in Harris Street, Pyrmont. Credit:Louise Kennerley It will likely be used in restorations works for Sydney's Town Hall, the University of Sydney and the Queen Victoria Building.

The Harris Street quarry could boost the government's yellow block supply by another 10 years, Mr Stratti said. Future projects, however, would boil down to a race for access to sites before they are entombed by development. "The important story here is the government needs to move quickly when these opportunities come up, and they need to look at what their part in making it happen needs to be," he said. More than century and a half ago, the Pyrmont peninsula, spanning the colonial streets of Ultimo to the headland, was pock-marked with quarries harvesting sandstone for the city's public buildings boom. From the mid-1800s until the early 20th century, quarrymaster Charles Saunders and his son ran the three most famous sandstone quarries in the area. They were named Paradise, Purgatory and Hell Hole by the stonemasons, a reference to the quality of the stone and the difficulty involved in extracting it. The best "paradise" stone was yellow block. It was prized for its strength and easy manipulation. When freshly harvested the stone is soft and grey, but it hardens as it oxidises and changes to a rich honey colour over a number of weeks.

Mr Stratti is confident more yellow block is buried beneath the Fish Market carpark and the derelict Rozelle Rail Yards – both of which have been slated for redevelopment. He has already discussed the Fish Market site with government representatives, framing it as the government's social responsibility to consider the harvesting potential before development occurs, he said. The Rozelle Rail Yards pose an even greater challenge. It is slated to be repurposed for the WestConnex motorway project. "There's opportunity there, but it's really hard to disrupt the pathway of development," he said. "When you've made a decision at a high level to put a freeway somewhere, try jumping in front of that."