Stone under the microscope – Sandstones from south-east Queensland

The sandstone industry in south-east Queensland currently boasts at least 15 operators most of whom are concentrated in and around Helidon, a little township located nearly 80km west of Brisbane. Collectively, these operators account for the majority of the dimension stone being produced in QLD. Small operations relative to those at Helidon also occur around the Warwick district to the south of Helidon, Murphy’s Creek between Helidon and Toowoomba, and another quarry and processing facility has recently been established between Beaudesert and Boonah.

Historically, the use of QLD sandstone for serious construction commenced in the 1860’s with quarries at Albion providing stone of variable quality. Westward extension led to the commencement of quarries at Goodna and Woogaroo and although coarse-grained the sandstone saw use in some prestigious buildings, e.g. Parliament House. Brownish sandstone was discovered near Helidon before the turn of the century and many quarries there have produced large volumes of stone for domestic and export use. The University buildings at St Lucia and City Hall are excellent examples of the durability of this stone.

Today the sandstone industry is quite mechanized and with crawler tractors, diamond wire saws, large diameter toothed blades on excavators, and Korfmann chainsaws extracting the bulk of the stone.

The commercial sandstones of south-east QLD were deposited as fluviatile sands during the formation of the Clarence-Moreton Basin. The timing of this deposition (Early Jurassic to Late Triassic) is close to 200 million years (which corresponds roughly with the appearance of the early dinosaurs).

Because sandstone is formed by the deposition of eroded, fragmented rock particles in continually changing hydraulic conditions, and then modified by post-depositional processes such as lithification, diagenesis and pore fluid activity it is hardly surprising that there may be many varieties of sandstone within the one quarry. Not only are there variations in structure, texture, and composition but also in colour. In addition, appearance can also be controlled during processing by the way the sandstone is cut with respect to its structure. A number of the quarries have a highly distinctive, speckled brownish variety that distinguishes Helidon sandstone from all others of the world. In Sharp contrast, the principal sandstone from near Beaudesert, about 80km south-west of Brisbane is a remarkably uniform medium-grey coloured stone that is almost indistinguishable in appearance from the sandstone Pietra Serena that has been quarried for over 400 years in Tuscany, Italy.

…..The application of sealers to sandstone paving is one area that tends to have problems. Home-owners and commercial operators are frequently advised by the salesmen to seal sandstone around pools and decks, especially in QLD. Within months there is a frequent incidence of failure with the sandstone delaminating, the arrises spalling or the surface pitting. Usually the quality of the sandstone is brought into question; however, failure is mostly due to the contrasting physical properties of the sandstone skin containing the sealer, or the migration of salts through the sandstone and meeting a barrier (the sealer).