Brisbane tuff


Brisbane tuff is a type of rock, formed as a result of a volcanic eruption. As the name suggests, it is a type of tuff found in Brisbane, Queensland, Australia. It is a form of welded ignimbrite. Brisbane tuff comes in a variety of colours: pink, green, blue and purple. The different colours are due to the extent of oxidation of iron and manganese.
It is often incorrectly described as porphyry.

History

Brisbane tuff began to be used during the period when Captain Patrick Logan was the commandant of the Moreton Bay penal colony.
Brisbane tuff is found in various parts of Brisbane and was quarried extensively in the early history of Brisbane at the Kangaroo Point Cliffs and the Windsor Town Quarry Park for use in construction of Brisbane's earliest buildings.

Geology

Brisbane tuff was formed by the compaction of volcanic ash more than 226 million years ago. It displays pyroclastic flows of rock fragments deposited as the volanic ash was forming. Layers of Brisbane tuff can be over thick.
It is a form of welded ignimbrite. Brisbane tuff comes in a variety of colours: pink, green, blue and purple. The different colours are due to the extent of oxidation of iron and manganese.

Construction

Brisbane tuff has been used in the construction of the following Brisbane buildings, many of them now heritage-listed:
Benedict stone is a mixture of cement and crushed Brisbane tuff used on building facades as an alternative to full stone construction. It was manufactured by Benedict Stone Pty Ltd which was established by Roman Catholic Archbishop of Brisbane, James Duhig, to manufacture the stone required for the Holy Name Cathedral, Fortitude Valley. The product was developed at the turn of the twentieth century by American manufacturer, Benedict. Duhig obtained a licence from America and opened the Benedict Stone works at Bowen Hills on 9 August 1929. In February 1930 Colonial Mutual Life advanced Duhig a mortgage on his properties which included the stone works. A mutually-dependent relationship developed between CML, Duhig and Jack Hennessey, architect. CML used Benedict stone to build a number of their Australian offices, ensuring some of their mortgage was repaid and employed Hennessey and Concrete Constructions Ltd, Brisbane.

Tunnelling

The extent and hardness of Brisbane tuff deposits has often been a barrier to building tunnels in Brisbane due to its 100–150 megapascal strength. However, since 2007, advances in tunnel-boring equipment with tungsten carbide cutting heads has enabled a number of major tunnels to be constructed in Brisbane, e.g. the Clem Jones Tunnel which passes through the Kangaroo Point area.