Important minerals in Maori culture included greenstone and obsidian; hard dense rocks for adzes, like the hardened argillite found alongside serpentine in Nelson; and natural pigments, such as black manganese oxides, blue vivianite, or pukepotu (an iron phosphate), and red and yellow ochres – kokowai – (the iron oxides hematite and limonite). More recently, non-metallic minerals of these types, now termed “industrial”, have become increasingly important, and their production and uses are expanding rapidly.
The greatest single output, £10 million worth, is of those materials (crushed rock, gravel, and sand) that are used in the booming constructional industries of roading and building. Similarly widely used bulk materials are clays for brickmaking, crushed limestone for agriculture, and limestone and marl (papa) for cement in the seven New Zealand works. Many handsome local building stones are available – marble, granite and allied rocks, limestone, serpentine, ignimbrite, and many darker volcanic rocks.
Lesser known minerals are perhaps the more interesting, however. Some rhyolitic volcanic rocks of the central North Island, known as “perlites”, have the property of swelling as much as 10 times when heated to about 1000° c. Perlite is used for plastering, sound insulation, and even as an artificial soil. The large volcanic eruptions that took place at Taupo somewhere about A.D. 200 caused large quantities of pumice, the natural lightweight material, to be carried downstream by the Waikato and Wanganui Rivers. Nearly 50,000 tons are quarried each year at Horotiu and Aramoho to be used in sandsoap, scouring powders, and insulating material, and nearly 1,000 tons are exported. Fine pumice, deposited along more ancient courses of the Waikato River, is worked principally as a filler at Takanini and Hunua near Auckland.
Sulphur occurs around many hot springs of the volcanic zone from Taupo to White Island, and 22,000 tons have been mined. Little now remains, nor are reserves of pyrite (iron sulphide) known to be high anywhere – the best known occurrences being 15–20 million tons of iron sulphide near Thames, averaging 7–8 per cent sulphur.
At Parengarenga Harbour, in northern Northland, brilliantly white dunes of pure quartz (silica) sand make an area of 4 sq. miles look like a permanent snow field. Over 50,000 tons from here, and 10,000 tons from Mt. Somers in Canterbury, are used each year, mainly for glass manufacture.
Two minerals have special uses because of the distinct forms of their crystals. Crystals of mica are flat, and can be parted into paper-thin sheets parallel to the flat surfaces. These sheets are used in electrical insulation, and for small unbreakable windows that have to withstand heat. Mica has been mined from pegmatites, i.e., granite rocks with unusually large crystals, at Charleston and in south Westland. Crystals of asbestos are thin and fibrous, and can be spun and woven like cotton to produce cloth and rope. The deposit at Takaka in Nelson contains only short fibres; 300 tons are used each year to make asbestos sheeting and “sidings” for building.
The large talc-magnesite deposits, also at Takaka, are exploited for the fertiliser industry. It has been shown to be technically feasible to separate both constituents: talc, which is the basis of talcum powder, and magnesite, which is the mineral form of magnesium carbonate. The related calcium-magnesium carbonate, dolomite, is available in large quantities in Ordovician rocks at Mt. Burnett, Collingwood.
Some 190,000 tons of phosphate rock were quarried from the Milburn-Clarendon deposits, Otago, in 1902–24 and 1943–4. Only a small amount of low-grade (10 per cent P2O5) rock remains there, or, as far as is known, anywhere else in New Zealand.
Many clays, of use other than for brickmaking, are quarried, and a high-quality clay used to make electrical insulators is actually mined underground at Kaka in Nelson. Fireclays, formed by the chemical leaching of rocks by acid waters beneath coal seams, are used to make the characteristically white firebricks at Huntly and Kamo. The even more intensely leached white “ball clays”, from Hyde and Idaburn in Otago, have been used for the manufacture of white earthenware, while pottery clays, formed by past hot spring alteration of the volcanic rock rhyolite, are quarried at Matauri Bay (Northland) and Mt. Somers (Canterbury). Clays that are capable of absorbing greases to an exceptional degree, and can therefore be used as decolorising and cleansing agents, are known as “fuller's earth”. They have been worked at Kamo (Northland) and are known at Gore, Southland. Bentonite, a clay which swells greatly in water to form a gelatinous mass with the consistency of grease, is known in a number of places near the east coasts of both islands. Good quality material can be obtained only with selective working. That from Porangahau is used as a drilling mud and in synthetic foundry sands.
Diatomite may appear claylike because of its fineness, but it is in reality an accumulation of myriads of external siliceous skeletons of the microscopic primitive plants called diatoms. This light powdery material is used as a source of silica, as an absorbent (e.g., of nitroglycerine), and as a filtering agent. It is worked in the Rotorua-Taupo volcanic zone and at Middlemarch, Otago.
Greenstone is found as boulders in the Taramakau and Arahura Rivers in northern Westland, in rivers draining west and south (e.g., the Dart) from the Olivine Range in southern Westland, and from Milford Sound. Its close relative, serpentine, is being used increasingly in New Zealand's fertilisers, particularly because serpentine superphosphate is free flowing, an important factor in aerial topdressing. A number of deposits in southern Northland near Te Kuiti, and east of Nelson, and at Mossburn in Southland, yielded over 160,000 tons in 1963, while a huge deposit is being opened up at the most northern point of the North Island – Kerr Point.
Salt, worth over £1 million, has been obtained by solar evaporation at Lake Grassmere, Marlborough, since 1952.