The geological formation of New Zealand Jade (Pounamu)

 

Jade is a semi-precious mineral divided into two types: Jadeite and Nephrite.

In New Zealand, there is only Nephrite Jade.

 

Jade is a metamorphic mineral, created under the earth's crust from high heat and pressure. It is the interaction of two straight fibered minerals, actinolite and tremolite, dancing together in a liquid form to create an interwoven matrix that is similar to the structure of chewing gum or a completely tangled rope. This is what gives the stone its special ability to be shaped and carved into intensely detailed and woven objects defying the ability of other stones.

 

Once fused underground, it makes its journey to the earth's crust.  Massive seismic events push these pockets of nephite to the earth's surface. Once these seams are closer to ground level, they commonly appear in a vertical formation. They are then exposed through glaciation and the cutting of water from the movement of rivers and heavy rain, rolling and smashing down the rivers, until some reach the ocean. These fragments of stone wash onto the beaches perfectly tumbled by the natural abrasion of its journey rubbing on other stones and rolling in the sand.

 

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How is Jade found ?

 

Jade can be found in a number ways depending on which stage of the natural process it is in.

 

In situ - This stone is still attached to the reef,  some of these reefs are exposed and visible to the eye, while others are covered by soil and bedrock. Mining, when done on a commercial level, requires machinery, large core drills and wire saws. Jade has only been mined in this way for commercial purposes and is most common in Canada.

 

Alluvial - Once the stone has come free from the reef it will travel, depending on the landscape, either across the plains by the glaciation or down the rivers in the moving water. These stones over time stretching thousands of years can develop oxidation. This is where lots of the stones with orange or red skin can come from. As the oxygen eats away at the stone, the colours will change and some of the well known characteristics will appear. These stones can range in size to being able to fit in your hand to being as big as a semi truck.

 

Seed - In some cultures this stone is the most prized of them all, the top quality seed jade has no skin, and is pure the entire way through with the same flawless consistency throughout. This type of stone was most commonly used along with much of the Alluvial jade by the indiginous people of New Zealand due to its availability pre machine era. These stones are found in the rivers and on the beaches where the jade bearing rivers connect to the Tasman Sea. Though some of the rarer stones can be homogeneous, single colour and pure or close to without grain, others offer a variety of textures, colours, skins and inclusions depending on the quality of the stone when it was formed.

 

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Where is Nephrite Jade found?

 

New Zealand, Canada, USA, Australia, China, Russia, Korea, Yemen, Afghanistan, Indonesia, Turkey, Switzerland.

 

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What about Jadeite and how is it different?

 

In 1863, the French mineralogist Alexis Damour distinguished Nephrite from Jadeite.

Jadeite is formed in metamorphic rocks, under high pressure and relatively low temperature conditions (Formed at the subduction zone, where tectonic plates move under another). 

While Nephrite consists of a microcrystalline interlocking fibrous matrix (Like a chewing gum), Jadeite is a microcrystalline interlocking growth of crystals (Like honeycomb) . Beside their formation, their chemical structure is also different.

While Nephrite has a hardness of 6.0 to 6.5 on the Mohs scale, Jadeite is slightly harder,  between 6.0 and 7.0 on the Mohs scale. But this does not make Jadeite more resistant to breakage. On the contrary, because of its fibrous composition, Nephrite is tougher and more resistant.

Despite this difference, it Is well known that Jadeite is a more precious and rare kind of Jade. It also provides us with a larger pallet of color than Nephrite such as purple, blue, red etc...

It is found in Guatemala, Burma (Myanmar), Japan. 

 

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What is Marsden Flower or Flower Jade?

 

New Zealand’s most famous variety of jade is ‘Marsden Flower’, this stone is found in a particular jade field south of Greymouth focused around the New River approximately 10km South of Greymouth township. 

 

The rich colour changes found in the stone from green to yellow are due to the unique way in which it was formed. While still underground, the stone is formed with holes and cracks left in it. It takes a second wave of heat and pressure which finally fills the remaining holes that were left the first time. The immense heat then fuses the stone into one, the highest quality of these stones have little change in the hardness in the differing colours. The lower quality forms of these stones can have huge changes in the hardness between the colours which could result in  an inferior weapon or tool if the stone was to break, and is challenging for the carver to work in modern day Jade artistry.