Almost all the rocks and minerals in New Zealand are found elsewhere in the world, and have been given internationally accepted names. But New Zealanders also have names for a small number of rocks that are distinctive or important.
Rock or mineral?
In the chemical sense, a mineral is a naturally occurring inorganic substance with a definite composition and structure. Quartz, with composition SiO2, is one of the most common minerals. All rocks are made of two or more minerals.
New Zealand does not have a designated national rock, but if one was ever chosen it would have to be greywacke. This drab grey stone is found everywhere in New Zealand – on the mountains, in the rivers, on the beaches. It consists of layers of hard, muddy grey sandstone alternating with thinner layers of darker mudstone (argillite). Technically the term greywacke refers to the sandstone (wacke is a German name for a type of sandstone), but it is also used as a general term for the entire rock.
Greywacke (Grauwacke) was first used in the 18th century to describe rocks in the Harz Mountains of Germany. Ernest Dieffenbach, a German scientist who travelled widely in New Zealand between 1839 and 1841, was the first person to use it for local rocks. English geologists regarded greywacke as an uncouth foreign term, but it was adopted in Scotland. Archibald Geikie’s Text-book of geology, published in 1903, gave descriptions of greywacke, and helped persuade New Zealanders that it was an appropriate term for their most widespread rock.
Greywacke is pronounced ‘greywacky’. Children’s author Lynley Dodd, known for her rollicking words and rhythms, used it in a picture book about a cat named Slinky Malinky, who spends his nights hobnobbing with his friends Greywacke Jones, Butterball Brown and the rest of the gang.
In the 1960s some geologists argued that the term greywacke was vague and imprecise. A subcommittee of the Geological Society recommended that it be dropped, but this was widely ignored. The term is possibly used more widely in New Zealand than anywhere else in the world.
The terms papa or papa-rock are used for the widespread soft, blue-grey mudstone or muddy sandstone.
Although the word papa is of Māori derivation (meaning earth), by the mid-19th century it was being used by Pākehā writers referring to mudstone, and in 1905 it was nicely summed up: ‘The Papa Rock, of which many of the cliffs in the bush country of New Zealand are formed, is really a very hard, blue clay … It lies in distinct strata, and when the wet penetrates to one beneath, the surface of this latter becomes as slippery as glass’. 1
The rock known as papa was deposited on the sea floor over the last 15 million years, then later uplifted. It is relatively soft because it has never been deeply buried or compacted. For engineering purposes, papa is classified as ‘soft rock’ or ‘engineering soil’ because it has the physical properties of unconsolidated soil rather than rock.
Pounamu is the Māori name for New Zealand jade (also called greenstone), prized for jewellery, tools and weapons, and widely traded. Although the term greenstone was generally used by Europeans, it is gradually being dropped in favour of pounamu.
In New Zealand, pounamu is found only in the South Island, and the name refers to two different minerals. Nephrite, the more common form, is a calcium magnesium silicate belonging to the amphibole group. It is found in the area close to Hokitika on the West Coast, and other sites. Bowenite, found only at the entrance to Milford Sound, is an iron magnesium silicate that is an unusual, translucent form of serpentine.
This hard, flinty form of argillite, from D’Urville Island and other South Island localities, was valued by Māori for making adzes, and widely traded. The name was originally used by archaeologists.
Adzite occurs along narrow zones between argillite and serpentinite. The argillite has been soaked in hot fluids which have reacted with the rock – a process called metasomatism – to impart the flinty nature to the adzite.