Tuesday, 21 April 2015

Kawau Island copper mines

Visited Kawau Island off the east coast of New Zealand in the Hauraki gulf last weekend. In 1844 copper was discovered on the Island and a mine was set up next to the coast. The chimney you see below is the engine house that housed a big steam engine to pump water out of the mine.

https://farm1.staticflickr.com/7/7495253_6ee384681d_o.jpg
Here is the description of the history of the site.

http://www.svfullmonty.com/?p=8550
I loved to see the amazing copper carbonate deposits around the copper mine and on the rocks around the area.

The rocks around the site were clearly a greenish-blue copper carbonate colour.



 However the rocks around the cave entrance were more of blue colour.

This indicates the fresh water around the cave, probably flows over the rocks when it rains, is hydrating the copper and giving rise to the classic Cu2+ colour.

The basic copper carbonate is green-blue colour and is called Malachite (Cu2CO3(OH)2).
http://upload.wikimedia.org/wikipedia/commons/b/ba/Malachite-153552.jpg
 The hydrated copper carbonate is a blue colour and is called Azurite (Cu3(CO3)2(OH)2).
http://upload.wikimedia.org/wikipedia/commons/f/fa/Azuritepigment.jpg
Azurite is broken down into Malachite over time. Here is an excellent picture of a rock caught during the transition.

https://www.facebook.com/TheEarthStory/photos/a.352867368107647.80532.352857924775258/783031718424541/?type=1
Sarah Thompson in the Photon Factory works on pigments and their photo degradation. So I was interested to see if this breakdown is important for Azurite pigments.
Raphael, Madonna and Child Enthroned with Saints, The Metropolitan Museum of Art
Sure enough in Raphael's Madonna and Child Enthroned with Saints the Virgin's mantle is darkened and a green colour due to Malachite where orginally it would have been a dark blue Azurite.

A painting with it particulary well preserved is Hans Holbein's Lady with a Squirrel and a Starling.

Hans Holbein the Younger, Lady with a Squirrel and a Starling, National Gallery, London
 It was a great day and the views from the boat were well worth the trip.



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