Lyttelton Harbour, Lyttelton, Banks Peninsula, Christchurch City, Canterbury Region, New Zealandi

Regional Level Types
Lyttelton Harbour	- not defined -
Lyttelton	Volcanic Field
Banks Peninsula	Peninsula
Christchurch City	City
Canterbury Region	Region
New Zealand	Country

This location was originally entered onto Mindat for tridymite, which is a polymorph of silica, occurring as tabular white or colourless hexagonal crystals in cavities in felsic volcanic rocks.

Julius von Haast first picked up a rock about one kilometre east of the Lyttelton town site, and was subsequently identified as tridymite by Professor Ulrich. P. Marshall in 1893 launched an in depth study on the location.

Marshall states tridymite is common in the upper cliff, above the Lyttleton to Sumner Road, facing Lyttelton Harbour, and a smaller cliff bordering the water itself, one kilometre east of Lyttelton. The cliffs are readily seen from the road, are whitish, or red-brown weathered by oxides. Tridymite was said to have been abundant in 1893, and there is nothing to indicate specimens may still not be available. However, the countryside is steep, at times vertical, so accessing them is another matter. The 2011 6.3 magnitude earthquake was centred near this location, and may have made cliffs and steep slopes unstable.

Cavities in the rocks contain glass clear tridymite hexagonal crystals. Sometimes the tridymite will completely fill up small cavities. Host rocks contain large plagioclase crystals, surrounded by a mantle of orthoclase or sanidine. Magnetite is said to be common, and apatite needles. The sanidine occurs as blue-grey to grey crystals, and granular aggregates, with Carlsbad or irregular twinning common. Rare globules of green glass is also noted.

Rocks of the Lyttleton Harbour and Banks Peninsula were formed from a series of volcanic eruptions (see under Lyttelton). The eruptions were predominantly basaltic, with associated andesite and trachytes, with minor rhyolite. The volcanic activity occurred in the Late Miocene and possibly extended into the Early Pliocene. There are four volcanic groups, all of which are within the Māui Supergroup (Mortimer, 2014).

Other Regions, Features and Areas containing this locality

References