Hukatere Volcano, Hukatere Peninsula, Kaipara District, Northland Region, New Zealandi

Regional Level Types
Hukatere Volcano	Volcanic Center (Extinct)
Hukatere Peninsula	- not defined -
Kaipara District	District
Northland Region	Region
New Zealand	Country

Hukatere Volcano is a small (4Km diameter) early Miocene volcano on the western side of the Hukatere Peninsula. It consists mainly of pillow lavas and submarine flows that are mostly basaltic andesite. Access is only available through private land (permission must be obtained) or via boat to the coastal exposures.
Some of these rocks have chilled, glassy margins (tachylite) and have been altered to a greater or lesser degree to palagonite in colours ranging from pale yellow to deep reddish-brown.
Cavities and fractures in the rock contain a variety of zeolites.
Heulandite-Ca is commonly found as small upright rectangular plates with a heavily textured surface or sometimes as pillow-like masses also with a textured surface that looks similar in appearance to gyrolite. Less commonly heulandite-Ca is found as more typical platy, trapezoidal crystals. In some cases, they cover large fracture surfaces in the rock.
Clinoptilolite-Ca seems to be quite rare but occurs as very clear aggregates with many, complex crystal faces. It is usually found in close proximity to heulandite-Ca and the two will sometimes occur in the same cavity.
Erionite-Ca is found as small hexagonal prisms with a flat termination, covering cavity walls and fracture surfaces. Rarely, erionite-Ca forms barrel-shaped crystals with a domed and complexly stepped termination.
Offretite is present and is similar in appearance to erionite-Ca but seems to be clearer and glassier with a higher lustre – almost adamantine.
Chabazite-Ca is found as glass-clear crystals, frequently as complex penetration twins. They range in colour from perfectly colourless to yellow, orange, slightly smoky to clove brown.
Phillipsite-Ca has several different forms ranging from clear, blocky crystals to small, pointed crystals which often seem to be partly etched and altered with a white coating. Morvenite twins and Perier core-bit twins have been found and so have pseudohexagonal crystals.
Paulingite-K is perhaps the most interesting discovery at this site and is probably the first time paulingite has been found in New Zealand. It is extremely uncommon and is found as very small and clear dodecahedral crystals usually dotted on clay cavity linings and very rarely suspended on thin clay threads. Paulingite crystals from this area are rarely more than 0.1mm across and are often so clear they are almost invisible – best seen when light reflects off the trapezoid faces.
Manganese oxides are frequently found as black, brown, or slightly golden scabs and botryoidal crusts or as coatings on zeolite crystals. Rarely manganese oxide is found as distinct, resplendent blackish red blade-shaped crystals.
Gypsum is uncommon and is found as small, clear clusters of crystals or dendritic growths. They are the final mineral to form in cavities.
Primary minerals in the andesite are feldspars, augite, diopside and olivine (which seems to be rather uncommon).
Feldspar sometimes occurs as crystals composed of two zones – an inner zone (possibly plagioclase) and a thin clear outer zone (possibly albite). The inner zone of these crystals is very frequently partially to completely dissolved by hydrothermal fluids, leaving the outer zone intact. When some of these rocks are split open, they crack through these feldspar crystals revealing a white crumbly interior of alteration products such as kaolinite, anauxite etc. With a little cleaning using pressurised water, a thin transparent mould is left behind showing the complex shape of the highly twinned feldspar crystals which made up the inner core.
Magnetite is very uncommon and appears as tiny octahedra in alteration debris of dissolved felspar crystals (they were probably inclusions in the feldspar).
Palagonite is very common as an alteration product of basaltic/andesitic glass resulting from chilling of lava erupted into seawater. It consists of smectite group clay minerals, zeolites, oxides of iron etc and is present in two forms - fibrous palagonite which is yellowish soft powdery material sometimes with small zeolite crystals dispersed throughout it.
The other form is palagonite gel, which is soft, waxy and translucent, ranging in colour from yellow, orange, red to deep brown. Intense orange to red palagonite gel seems to be influenced by manganese oxides which are usually found nearby.
Clays occur in several colours (pale blue, grey, white, yellow, orange) and form cavity linings and strange structures like tangled noodles, thin strands, columns, stalactites etc. These are probably smectite group minerals such as montmorillonite.
Glass is mostly found as tachylite and although it is a volcanic glass, it is not at all like obsidian in appearance – it is very impure in comparison and is just barely translucent (usually dark blackish brown) with a somewhat granular texture. However, glass is sometimes found as deep red translucent fragments embedded in palagonite gel.

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