Limestone is a rock composed mainly of lime (calcium carbonate – CaCO3), almost always formed from shelly material. Some limestones are very fine-grained, originally being a limey ooze on the sea floor, but in other rocks large shell fragments can be seen. Limestone is widespread in New Zealand, and formed mainly in late Eocene to Oligocene time, 25–40 million years ago when much of the New Zealand region was submerged beneath the sea.
The hardness of limestone depends on how deeply it has been buried. Softer rocks such as Ōamaru stone have been compacted, but can still be carved and cut with a saw. Most other limestones have been more deeply buried. The calcium carbonate has crystallised in the pore spaces to form a hard, dense rock that can be polished. When limestone is deeply buried and heated it recrystallises so that the original shelly material cannot be recognised, and it is then called marble.
Ōamaru stone
New Zealand’s most important building stone is a very pure, massive limestone, soft enough to be readily sawn and worked. It is composed mainly of microscopic bryozoa that accumulated as a submarine shellbank in the Ōamaru area. Because of its purity, it is mainly white. Small amounts of volcanic ash give the lower part a yellow tinge, and result in a poorer quality stone.
Whitestone City
With pride in its heritage of neoclassical buildings, Ōamaru has adopted the name Whitestone City for promotional purposes, and holds an annual heritage week in November.
Quarrying began about 1860, and Ōamaru stone was obtained from many different quarries inland and south of Ōamaru. Virtually all stone used for building since the 1940s has come from Taylors or Parkside quarries at Weston, and the latter still works the purest limestone. To extract the stone, it is cut into 2-tonne blocks by a chainsaw cutter, and broken out with a fork-lift loader. In an adjacent factory these blocks are cut into slabs by large circular saws.
The ease of dressing Ōamaru stone made it popular for buildings throughout New Zealand. It has been widely used for decorative work around windows and doors, as well as carved pillars and gargoyles. After several decades it tends to weather and flake. Many older buildings have needed cleaning and repair, but this can now be largely avoided if the stone is sealed.
The hardness of limestone depends on how deeply it has been buried. Softer rocks such as Ōamaru stone have been compacted, but can still be carved and cut with a saw. Most other limestones have been more deeply buried. The calcium carbonate has crystallised in the pore spaces to form a hard, dense rock that can be polished. When limestone is deeply buried and heated it recrystallises so that the original shelly material cannot be recognised, and it is then called marble.
Ōamaru stone
New Zealand’s most important building stone is a very pure, massive limestone, soft enough to be readily sawn and worked. It is composed mainly of microscopic bryozoa that accumulated as a submarine shellbank in the Ōamaru area. Because of its purity, it is mainly white. Small amounts of volcanic ash give the lower part a yellow tinge, and result in a poorer quality stone.
Whitestone City
With pride in its heritage of neoclassical buildings, Ōamaru has adopted the name Whitestone City for promotional purposes, and holds an annual heritage week in November.
Quarrying began about 1860, and Ōamaru stone was obtained from many different quarries inland and south of Ōamaru. Virtually all stone used for building since the 1940s has come from Taylors or Parkside quarries at Weston, and the latter still works the purest limestone. To extract the stone, it is cut into 2-tonne blocks by a chainsaw cutter, and broken out with a fork-lift loader. In an adjacent factory these blocks are cut into slabs by large circular saws.
The ease of dressing Ōamaru stone made it popular for buildings throughout New Zealand. It has been widely used for decorative work around windows and doors, as well as carved pillars and gargoyles. After several decades it tends to weather and flake. Many older buildings have needed cleaning and repair, but this can now be largely avoided if the stone is sealed.
