Found rock on river bed

[4meter 200]

On 7/27/2018 at 5:02 PM, Bedrock Bob said:

O.K here is what I am seeing. I hope we will get some discussion on this so you can get some other perspectives.

The stone is a high silica rock. You can see it is glassy and vitrified material. It takes a polish. The constituents are crystallized.

The pockets are where minerals popped out and left a socket. 

It has been polished and tumbled in water for some time. 

It looks to be olive green in color with some reddish specks in there. You can see subtle color changes indicating different colored granules in the matrix. You cant see the individual grains too well but the texture suggests a granular stone that has been smoothed down. It is not pitted (other than the obvious sockets). It was roughly broken and is not completely worn smooth. It is comprised of hard jagged crystals of high silica minerals.

I think this is a pegmatite. It had some inclusions in it and they have released in weathering leaving these pockets. Everything has been smoothed and blended by water action.

Pegmatites often are olivine rich and contain inclusions like garnet, feldspars, gemstones, etc.etc.  They are a type of granite and this may actually be a granite. I am not sure the distinction between the two is really important here. I think either is appropriate but we might get some discussion on that. (There are lots of guys here that are much better at ID than me and I try to keep them pissed off. That way if I am wrong they jump to correct me).

A pegmatite with olivine came from deep in the earth. Probably from some volcanic event. I am not familiar with your local geology but granites are common mountain building rocks. And glacial action delivered a bunch of rocks to those lake regions so I suppose a rock may have travelled a long way on ice to get to your river.

Or someone else could have carried that rock and dropped it in the river. If the rock is what it is to you, it makes sense it could have been that to someone else, que no?

It is a cool rock. I would have picked it up too. The pattern the pockets make are almost braille. It looks like they may fit fingertips. At 2" it is just the right size for a pocket stone.

Make yourself a medicine bag and carry it with you. I will post a photo of the stones in my medicine bag on this thread after we have a chance to discuss your stone. 

Anyhoo, that is my identification and why I think that. I hope we have some other rockhounds chime in. It is a special rock no matter what it is. Far rarer than gold for sure and it deserves a discussion. This group may not ever see another like it and I think we should give this our best shot. 

The part about olivine is incorrect.  Olivine is never found in pegmatite or granitic rocks (high silica content).  It is only found in certain mafic rock (low silica content) types such as basalt, gabbro or peridotite among others.

Mr. Fisher - take a brass brush to a small spot and give it a vigorous rubbing to see if the "green" comes off and see what, if any color is exposed.  

When I enlarged the image of the "green" rock I can see that the light colored "holes" or dimples have small, sim-angular gains of material in it.  It appears that the dimples are a secondary mineral, filling the dimples on the rock, with embedded sand grains, thus may not be part to the "green" rock.  It could be the remains of a natural cementing agent when this rock was part of a natural rock layer.  Now most of that cementing agent has  been worn away by the action of water leaving what we now see.

Black River WI, Ooo anywhere other than WI;  so much material dumped glaciers to be found up there.

Edited July 29, 2018 by 4meter

[Saul R W 741]

On 7/28/2018 at 10:54 PM, Mr.Fisher said:

Should I run it under tap water?

Water won't hurt it, not unless it goes back to banging about in a creek bed for many thousands of years..