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henderson_s_quarry_ngongotaha

Henderson’s Quarry, Ngongotaha

Henderson’s Quarry is a major excavation in volcanic rock on the eastern side of Mount Ngongotaha, near Rotorua on the North Island of New Zealand.

The quarry is made up of several rock types including pumice, obsidian and rhyolite. Crystalline minerals occur in lithophysal cavities in the rhyolite zone.

Henderson’s Quarry, Ngongotaha

One of the field trips conducted as part of the 2007 New Zealand Micro Mineral Symposium and Joint Australian Mineralogical Societies Seminar was to Henderson’s. On this trip, many of the minerals previously identified were found, including some very nice specimens of the rare silicate osumilite-(Mg).

Collecting took place in a number of areas in the quarry, but the most interesting finds, including the osumilite, were from boulders on the edge of one of the upper benches.

Collecting is only by permission.

Henderson’s Quarry, Ngongotaha


The Minerals


Augite

Augite, Henderson’s Quarry, Ngongotaha

Found as single tiny needles on tridymite.


Edenite

Edenite, Henderson’s Quarry, Ngongotaha

Most commonly found as thin white flexible hairs, sometimes with hematite balls attached.


Fayalite

Fayalite, Henderson’s Quarry, Ngongotaha

Ubiquitous, next to tridymite, the most commonly found mineral. Many are altered. In an extreme case, a few specimens were found with what appears to be micaceous edges and partially coated by hematite balls (see photo).


Hematite

Hematite on edenite, Henderson’s Quarry, Ngongotaha

Hematite, Henderson’s Quarry, Ngongotaha

Common as thin or thick tabular hexagonal crystals, as balls on edenite, or as reddish-brown coatings.


Osumilite

Osumilite, Henderson’s Quarry, Ngongotaha

Found in one boulder only as dark green hexagonal crystals to 7 or 8mm long.


Phlogopite

Phlogopite, Henderson’s Quarry, Ngongotaha

Common as orange-brown thin plates.


Pseudobrookite

Pseudobrookite, Henderson’s Quarry, Ngongotaha

Uncommon as small prismatic crystals.


Titanite

Titanite, Henderson’s Quarry, Ngongotaha

Rare as tiny yellow-orange crystals.


Tridymite

Tridymite, Henderson’s Quarry, Ngongotaha

Abundant as cavity linings of colourless to white hexagonal crystals.


Other minerals recorded

Ferro-edenite, ilmenite, magnetite, quartz and richterite.


References

Howard, D.G., Grapes, R. and Thornton, J., Vug Minerals in Rhyolite, Henderson Quarry, Mt Ngongotaha.

Sorrell, S.P. (2008), A report on a trip to Henderson’s Quarry last October, Australian Mineral Collector No. 6.

henderson_s_quarry_ngongotaha.txt · Last modified: 2016/07/20 08:42 by crocoite