Story: Rock and mineral names
Page 4 – Mineral names – 2
Wairakite – CaAl2Si4O12.2H2O
Exploration for geothermal steam in the 1950s led to detailed studies of the minerals and rocks in thermal areas. Alfred Steiner, a pioneer geothermal scientist, discovered and named wairakite in hydrothermally altered drill cores at Wairākei. Wairakite occurs as veinlets and cavity fillings. It has subsequently been found worldwide.
Most wairakite occurs as microscopic crystals, but well-crystallised specimens have been found inside casings in a steam well.
Wairauite – CoFe
Named after the Wairau Valley in Marlborough, this is a natural iron-cobalt alloy. It occurs as microscopic, scattered grains in serpentinite, often alongside awaruite. The grains rarely exceed 5 microns (0.005 millimetres) in diameter. Wairauite is the first New Zealand mineral to be identified by electron microprobe – the only possible means of analysis.
Akatoreite – Mn9(Si,Al)10O23(OH)9
A manganese-rich patch of chert and carbonate on the south Otago coast, near the mouth of the Akatore River, was found to contain tiny crystals of a fibrous yellow mineral which was hard to identify. In 1971 Peter Read and Tony Reay (geologists from the University of Otago) recognised this as a new manganese silicate mineral, which they named akatoreite. Although originally known only from the locality, it has since been recognised in Sweden, and is likely to occur elsewhere with manganese-rich rocks.
Motukoreaite – Na22Mg38Al24(CO3)13(SO4)8(OH)10.56H2O
A poorly cemented calcareous rock, informally called ‘beach limestone’, occurs at two places on the shore of Browns Island (Motukorea) in the Waitematā Harbour. In 1977 Kerry Rogers and colleagues from the University of Auckland analysed the fine-grained rock and recognised a new mineral, which they named motukoreaite. It occurs as a boxwork of tiny crystals, each about 3 microns (0.003 millimetres) across.
Motukoreaite has been recognised elsewhere as a low-temperature alteration product of volcanic glass.
Feruvite – CaFe3(Al,Mg)6(BO3)3Si6O18(OH)4
A new iron-rich variety of tourmaline found in a coarse-grained granitic rock on Cuvier Island off Coromandel Peninsula, was collected and analysed by J. D. Grice and G. W. Robinson in 1989. This mineral is part of the uvite group, and as it is rich in iron (Fe), it was named feruvite.
Coombsite – K(Mn,Fe,Mg)13(Si,Al)18O42(OH)14
A small area of manganese-rich rock at Watsons Beach on the south Otago coast (about 3.5 kilometres south of where akatoreite is found) contains brown patchy aggregates that include tiny brownish-yellow fibrous crystals. This new manganese mineral was described by Japanese mineralogists Teruhiko Sameshima and Yosuke Kawachi in 1991, and named for Professor Douglas Coombs of Otago University.
Ferroceladonite – K2Fe4Si8O20(OH)4
Ferroaluminoceladonite – K2Fe2Al2Si8O20(OH)4
In the 1990s, crystals from the Hokonui hills, east of Gore, were analysed by electron microprobe, a new technique for microscopic analysis. Previously the crystals had been identified as celadonite, a well-known mineral in altered volcanic rocks. Mineralogists knew that it had varying proportions of magnesium, iron and aluminium. However, the microprobe revealed two new minerals, which were named ferroceladonite and ferroaluminoceladonite. The crystals are extremely small: 1–2 microns thick (there are 1,000 microns in a millimetre).