Many of the heritage buildings in the Sydney area are composed, either wholly or in part, of local sandstone. On the basis of broad composition, colour and colour change, dimension sandstone can be classified into six groups. However, most Sydney sandstone buildings are composed of either/or both of (a) 'yellow block' sandstone and (b) quartz-rich sandstone.
The well-known Sydney 'yellow block' sandstone is a true dimension stone, which is grey when quarried, but oxidises and darkens on exposure to the atmosphere to a warm yellow-brown colour. Quartz-rich sandstone is white, grey or pale yellow in colour when freshly quarried and does not darken or change colour significantly on exposure to the atmosphere.