<p>Nephrite jade (nephritite) (14.8 cm across at its widest) from the Precambrian of South Australia.
</p>
<hr><p>Nephrite jade (nephritite) is a microcrystalline-textured metamorphic rock consisting of 1 or more amphibole minerals (tremolite to actinolite).  This rock is from the Cowell Jade, a para-nephrite jade deposit having large, lensoidal nephrite masses in tremolite-chlorite-epidote-zoisite-talc alteration zones along the margins of chloritized feldspar rock that has intruded dolomitic marble &amp; banded calc-silicate rocks (it also occurs in cross fractures).
</p><p>It took no less than four metamorphic events to get this rock.  High-grade metamorphism of the protolith occurred during the Paleoproterozoic, at 1.84 Ga and 1.78 Ga during the Kimban Orogeny.  The nephrite jade itself formed during late Paleoproterozoic recrystallization and replacement events during retrograde metasomatism at 1.70 Ga + early Mesoproterozoic alteration at 1.59 to 1.60 Ga.
</p>
Locality: Mount Geharty Jade Mines, Cowell Jade Province, Mount Geharty area in the Minbrie Ranges, Gawler Craton, ~20 km north of the town of Cowell, eastern Eyre Peninsula, South Australia.
<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/15018752488/">Nephrite jade (nephritite) (Cowell Jade, Proterozoic; Mount Geharty Jade Mines, 20 km north of Cowell, eastern Eyre Peninsula, South Australia)</a>