<p>Nephrite jade from New Zealand. (public display, Montana Bureau of Mines and Geology Mineral Museum, Butte, Montana, USA)
</p><p>Nephrite jade (nephritite) is a crystalline-textured to felted-textured metamorphic rock principally composed of one or more amphibole minerals (tremolite to actinolite, Ca2Mg5Si8O22(OH)2 to Ca2(Mg,Fe)5Si8O22(OH)2).
</p><p>The gorgeous slice of green nephrite jade shown above is from New Zealand's South Island.  New Zealand jade has long been collected as fluvial/alluvial clasts that were eroded from a segmented ophiolite called the Pounamu Ultramafic Belt.  Ophiolites are fragments of oceanic lithosphere (basaltic crust + uppermost mantle) that have been metamorphosed and plastered onto the edges of continental lithospheric plates by obduction (the opposite of subduction).  Pounamu nephrite jade has been interpreted as altered (tectonized) tremolite-rich rocks.
</p><p>Geologic unit: Pounamu Ultramafics
</p>
Locality: unrecorded/undisclosed locality in the South Island of New Zealand (but very likely a fluvial or alluvial boulder ultimately derived from the the Pounamu Ultramafic Belt)
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/47445767@N05">James St. John</a>
CC BY 2.0
<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/jsjgeology/24069093653/">Nephrite jade (Pounamu Ultramafics, Pounamu Ultramafic Belt, South Island, New Zealand) 1</a>