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Odd Green Rock


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I’m not much of a mineral person, but I came across this odd green rock. Any idea what kind of mineral this is?

 

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1 hour ago, grandpa said:

Possibly green moss agate.  Can't tell for certain from photo.


Caught my eye randomly. More of a fossil guy, but don’t see too many green stones hah. As an additional note, it’s a worn stone found on a beach in Massachusetts. My initial thought was Serpentine, but not based on much.

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Serpentine or Serpentinite would be my guess too.

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  • 1 month later...

One of the jades, maybe?  Nephrite or Jadeite?  Yes, sometimes Serpentine can look like that, like from the Franciscan Formation of the coast of California.  We have alot of this type of stuff here along the coast, but it is metamorphic.  A place called Jade Beach, CA is a popular place to collect such items.  Kinda looks like it, but I don't know the geology of Massachusetts. 

 

In California, we sit over a subduction zone, and to the east of the San Andreas Fault, we have alot of metamorphic materials, like schists, eclogite, serpentine, etc.  And interestingly, some of these share many of the same minerals, but can look very different because of the different combinations and portions of minerals they are composed of, PLUS the different temperatures at which they cooled, or different types and extremes of pressure they were exposed to. 

 

Look at this eclogite, very rare, only found in a few places on this planet.  It is called Christmas Tree rock

because reddish garnets sit within a green, schisty type of background (like ornamemts on a Christmas tree).

 

For myself, I prefer to call it chocolate chip rock, though if you never find a green chocolate chip cookie - don't eat it!  I collected this from one mile north of Jenner-by-the-Sea on Highway 1.  I was looking for it and knew I had found it when I saw something green and glittering on the hillside above me.  I really had to climb for it, but was richly rewarded with boulders of it!

 

 

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