Serpentine versus Jade; Washington coast rock

[southerly]

Serpentine is highly variable because it is a name given to a class of rocks serpentinites with variable histories (the source rocks that were serpentinsed) and variable amounts of serpentine geologists distinguish many types of serpentinites for example lizardite-serpentinie while us lapidaries just call it serpentine. It can range from flakey and soft MOHs 2 to hard hard and fracture free arounds mohs 5 to 5.5.

Nephrite and jadeite after form within or from serpentine deposits (jadeite always does) so they are often found together.

In the field when searching for nephrite in situ we tell the serpentine and jade apart by whacking each boulder with a hammer, most serpentine gives a dull thud. Jade has a very specific ring and the hammer bounces off it. Note that some of the harder serps and things like massive chalcedony can give a similar but not the same ring. Often in the field the serp looks much more jade like than the jade so visual appearance is misleading. One thing that is common in serpentine and I use for a diagnosis when people bring rocks to the club is its soapy feel in the hand.

[Mark]

Here's the link to the thread where Mike (mearic71) and me, posted pics of our green and blue and blue/green Massachusetts rocks which are thought to be Serpentine.

Mark

http://gemstone.smfforfree4.com/index.php/topic,17815.msg202280.html#msg202280

[trigon]

I used to collect Nephrite down at Jade Beach by Big Sur in California, where there is also lots and lots of Serpentine. The general rule 'in the field' was that if it would scratch with a good steel blade, it was Serpentine. If not, it was Nephrite.

[lithicbeads]

That rule dos not work in Washington as many jades are rather soft ( but x-ray diffraction tested as nephrite ) while some serps here are 5 hardness on the mohs scale.

[mearic71]

Hey Mark,
Hope you got some good pieces.
Mike

[tkcaz]

Lithicbeads, I would very much like to know what a "folded" slickenside is, and how you were able to identify that from the picture. Thanks.

[lithicbeads]

A classic slickenside would be largely planar with  parallel grooves between 1/8  and 1/16 inch deep . However many slickensides are made where the stone reacts to pressure that comes from various angles  with no angle predominant for a long time. This causes torque in the rock  and much less well developed slickensides. These are typically more like valley and ridges where the valleys are narrow and a weaker component of the serp , here usually thin asbestos stringers. The rounded ridges show a scraped polished quality that was caused by relatively transient movements. Serps endure lots of faulting  as do other subducted rocks and they absorb  lots of force by deforming very unlike brittle rocks which when the pressure is adequate snap and can cause more destructive movements. The precursor rock as pointed out is very important as is the degree of serpetinization which may not be complete. Serps can also transfprm themselves back to the original precursor rock with retrograde metamorphism as they rise from the subduction trench. The degree of hydration of the serp is also a large factor in it's appearance.

[tkcaz]

And you could see all that in a snapshot. Awesome.  Thanks!