Two types of chert are to be found in the Hauraki area. Those of the Coromandel Peninsula are derived from volcanic activity while the sedimentary cherts present on the islands of the Hauraki Gulf are eroding out of the Waipapa and Waiheke Series of geological formations which also produced the greywacke (see Fig. 12).
Known volcanic sources of chert within the Hauraki area include Kaitoke Valley on Great Barrier Island, Rings Beach near Kuaotunu, Black Jack and Otama, Manaia, Kauaeranga Valley, Whitipirorua and Great Mercury Island. Sedimentary sources include the islands of Kawau, Motutapu, Waiheke, Ponui and McCallums, the coast between Maraetai and Orere Point, and the Hunua Range. The material occurs as cobbles in stream beds and on beaches and erodes out from lenses within the sedimentary Waiheke Group (Moore Dm).
Some of the Coromandel chert may have been struck off outcrops (for example, T10/665 behind Otama) or extracted from hydrothermally altered rock at Hot Water Beach. However the high proportion of excavated chert with a weathered cortex indicates it came from streams and beaches.
Chert has been found in the majority of sites excavated, attesting to its importance as an every day multi-purpose material. Hammerstones of chert, present in at least one Tamaki site, and R10/31 on Motutapu Island, were used to make adzes, and chert adzes are not unknown, especially from sites of an early age such as Whitipirorua. It was most commonly used for drill points, used in the manufacture of other tools. Occasionally it was put to other uses—for instance at R11/1506, Tamaki, a chalcedony pebble with a natural hole at one end may have been used as an ear or neck ornament.
In a similar pattern to obsidian, chert was moved out of the Coromandel area possibly as far north as Houhora. However indications are that the sources were mainly of importance locally.
Other stone
Stone materials such as andesite, dacite, argillite, sandstone, diorite and petrified wood were used for a variety of tools. For instance andesite from the Coromandel Ranges and possibly Waiheke was used for adzes, flax beaters, weapons and large grinding slabs; diorite and tonalite used for hammerstones on Tahanga may have come from near Paritu, Stony Bay or possibly Cuvier Island (Moore 1982:40); petrified wood also found on the Coromandel Peninsula was used for fishing lures and abrading tools, and sandstone from various locations was used for hoanga to sharpen adzes and shape bone and stone tools. In addition many minor localised stone materials were also used in an opportunistic way—these include tuff, ignimbrite, rhyolite and various other volcanic and sedimentary stones.
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