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Author Topic: Can you identify this rock for me?  (Read 2961 times)

Offline Lor

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Can you identify this rock for me?
« on: 04/07/2010 06:38:12 »
i found this in the front yard not long after my brother in law put in a handrail along the walkway so i guess he dug it up. it looks like it was cracked in half and has layers but is contained. I'd love to know how it formed and what type of rock(s)? it is. i'm clueless but very curious regarding it's formation.I'm in Rhode island, and the soil is very rocky-if that helps.
 [:I]


 

Offline JimBob

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Can you identify this rock for me?
« Reply #1 on: 04/07/2010 19:27:09 »
Being found in Rhode Island does not mean that this rock came from beneath the surface of Rhode Island ORIGINALLY.

There is something called glaciation that brought a lot of stuff in from the north and west - rock stuff - sediment. However, this does not mean the rock pictured above could not have come form what forms the ground beneath your feet. It very well could have come from beneath your feet.

My Observations:

1.) The outer part is black - the inner part is white - D'oh! But there is significance to me in this.

2.) The outer layer is NOT evenly distributed over the white.

3.) WHY should there be a "tail" on this rock?

#2 rules out, in my mind,this being a "concretion," the obvious first conclusion when looking at the pictures.

SO whatisit????

To the west in Connecticut there is a feature called the Hartford Trough. It is full of Triassic Volcanics. But there are also two episodes of pre-Cambrian volcanic terrains of the same type on either side of the Hartford Trough, a failed rift full of basalts and slightly more silicate rich rocks that has on either side of it small extrusive volcanic vents.

SO - (and here is where everyone will pile on)  I suspect greatly that this is cored volcanic bomb. As one of my honors papers in my senior year, I did a thin section petrological study entitled "Cored Volcanic Bombs From the Raton Volcanic Region, Northeast New Mexico."

This area is a cluster of basaltic cinder cones with thick enough magma to allow explosive eruptions. As this is on the east side of the Rio Grande Rift System, it is in a very similar setting as the area you are in.

The way these "bombs" form is this: magma is forced up through the overburden. Near the surface pieces of the rock through which the magma moves are broken off and are incorporated into the magma. A rind forms around the country rock that is not of consistent thickness and this gets thrown out of the volcanic vent. As the outside is still mostly molten, the outside gets formed a bit bu passing through the air. That is why the "tail" fascinates me so much.

Ok - here I am

« Last Edit: 04/07/2010 23:07:17 by JimBob »
 

Offline Lor

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Can you identify this rock for me?
« Reply #2 on: 05/07/2010 02:35:57 »
Wow-that is interesting.Thanks for the detailed information(and no'size' cracks)JimBob.lol. I did know about the glaciers pushing rock southward and receding,Great lakes and all that-I'm pretty sure they deposited a slew of it right on this parcel of land-its very rocky and also has about a dozen boulders in the backyard.The hill I live on is probably all rock. I think I've got the bug now.I was in my yard all afternoon looking for strange rocks-lol
..here is a better pic of the tail just to be sure.and a scaled.
« Last Edit: 05/07/2010 02:46:38 by jazzderry »
 

Offline Lor

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Can you identify this rock for me?
« Reply #3 on: 05/07/2010 02:48:52 »
arg-can't get uploaded rt-heres the tail.
 

Offline Bass

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Can you identify this rock for me?
« Reply #4 on: 05/07/2010 20:24:15 »
Let's see if I can JB's target

Generally, rocks weather from the outside towards the inside.  I can't tell what the "white inner core" of this rock is- but I suspect the black outer rim is manganese oxide (pyrolusite-type mineral).  Which means basalt is doubtful for this rock.  Not so sure about the "tail" either.

But I agree with the rest...
« Last Edit: 05/07/2010 20:26:03 by Bass »
 

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Can you identify this rock for me?
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