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Author Topic: Help Identify Black Rock w/ Green Flecks  (Read 11574 times)

Offline gregstarling

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Help Identify Black Rock w/ Green Flecks
« on: 30/07/2009 14:47:27 »
I apologize for my first post being a question and not something of value, but I'm pretty desperate. My grandfather gave me this rock when I was a small child, and I've never known what it was. I live in Oklahoma, but the rock could have been from anywhere. Unfortunately, I don't have the ability to ask exactly where it came from.

It is pretty hard, is mainly black, but has large green fleck throughout.




Any help is greatly appreciated.

Greg


 

Offline RD

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Help Identify Black Rock w/ Green Flecks
« Reply #1 on: 30/07/2009 16:52:06 »
The green bits possibly olivine ?

[Bass & Jimbob are the resident geologists, you should await an appraisal from one of them them].
 

Offline Mazurka

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Help Identify Black Rock w/ Green Flecks
« Reply #2 on: 30/07/2009 17:23:04 »
That looks like a black basic matrix with olivine or sperpentenised olivine (olivine weathers really quickly).  Could be a bit oceanic crust from an ophiolite?
 

Offline gregstarling

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Help Identify Black Rock w/ Green Flecks
« Reply #3 on: 30/07/2009 17:26:04 »
thanks so much for the help so far. I know it's weird, but finally knowing what this rock is will be a huge childhood mystery solved
 

Offline RD

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Help Identify Black Rock w/ Green Flecks
« Reply #4 on: 30/07/2009 18:49:51 »
Could be local ...

Quote
The Geological Society of America (GSA)
South-Central Section–40th Annual Meeting (6–7 March 2006)

CRYSTALLIZATION DYNAMICS OF THE MT. SHERIDAN ROOSEVELT GABBRO, WICHITA MOUNTAINS, OKLAHOMA

Three texturally distinct rock types in the Mt. Sheridan Roosevelt Gabbro suggest distinct modes of crystallization. The vertically stratified pluton is composed of layered gabbro in the lower elevations (the growing cumulate pile) which is overlain by homogenous quartz gabbro (the active magma chamber). Felsic pegmatite is present, and locally abundant, throughout the pluton (see McEllen et al., this session). These three rock types, though texturally distinct, are genetically linked during crystallization of the magma chamber. Reverse zoning in plagioclase and the repetition of olivine-bearing and quartz-bearing rocks vertically within the pluton indicates the magma chamber received multiple mafic replenishments during crystallization (Lasco et al. 2004). Isolation and extreme fractionation of the mafic magma could produce a felsic melt that, if kept isolated from the active chamber, would be preserved as pegmatite.
http://gsa.confex.com/gsa/2006SC/finalprogram/abstract_99947.htm
« Last Edit: 30/07/2009 19:18:08 by RD »
 

Offline frethack

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Help Identify Black Rock w/ Green Flecks
« Reply #5 on: 30/07/2009 22:43:54 »
Agreed...looks like an olivine basalt porphyry

Back to the books and more academic self-flagellation
 

Offline JimBob

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Help Identify Black Rock w/ Green Flecks
« Reply #6 on: 31/07/2009 04:35:16 »
I TOLD YOU TO QUIT THAT, A-HOLE!

You just got over swine flu yesterday!!!!!
 

Offline JimBob

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Help Identify Black Rock w/ Green Flecks
« Reply #7 on: 31/07/2009 04:42:28 »
Oh - it is either olivine -- or diopside?
 

Offline Bass

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Help Identify Black Rock w/ Green Flecks
« Reply #8 on: 31/07/2009 05:03:53 »
I suspect the crystals are probably plagioclase feldspar.  Plagioclase phenocrysts are common in basalt/andesite porphyries.  Unlike olivine, plagioclase forms the long, lathe-like crystals similar to those in the photo.

There appears to be an olivine crystal within the large plagioclase crystal in the center of the second photo (poikilitic texture).
 

Offline Geoman69

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Help Identify Black Rock w/ Green Flecks
« Reply #9 on: 03/08/2009 20:41:24 »
From what I can tell, Bass is correct.  Olivine crystals tend to have a hexagonal cross-section, where those lath-shaped crystals are characteristic of Plagioclase.

The large crystals within a fine grained groundmass indicate two stages of cooling (cooled slowly enough for those large plagioclase crystals to grow, then was brought to a lower temperature where the groundmass didn't have time to form large crystals before it cooled).

The major constituents are likely pyroxene, ca-plagioclase and olivine.

Cool sample!
 

Offline coquina.rocks

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Help Identify Black Rock w/ Green Flecks
« Reply #10 on: 22/08/2009 13:47:28 »
Hi - I'm new here - I'll introduce myself later...
Is your rock magnetic?  It looks like cumberlandite, which happens to be the state rock of Rhode Island.

 

Offline saamsuun

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Re: Help Identify Black Rock w/ Green Flecks
« Reply #11 on: 20/11/2012 06:15:56 »
I apologize for my first post being a question and not something of value, but I'm pretty desperate. My grandfather gave me this rock when I was a small child, and I've never known what it was. I live in Oklahoma, but the rock could have been from anywhere. Unfortunately, I don't have the ability to ask exactly where it came from.

It is pretty hard, is mainly black, but has large green fleck throughout.




Any help is greatly appreciated.

Greg

This looks pretty close but im not sure of its gender , species , domain , DNA , or come whatever you may call it. we found it in anaheim ca. Home of Western " DisneyLand ". Orlando is eastern " DisneyLand ". Its very Purdy.
 

Offline Boogie

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Re: Help Identify Black Rock w/ Green Flecks
« Reply #12 on: 21/11/2012 16:00:52 »
Is there any chance saamsuun's specimen is a breccia?

If not, what disqualifies it?
 

Offline Bill S

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Re: Help Identify Black Rock w/ Green Flecks
« Reply #13 on: 21/11/2012 17:41:21 »
Quote
Is there any chance saamsuun's specimen is a breccia?

Could be, but some of the larger bits look bore like crystals than clasts; especially the one at top left.
 

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Re: Help Identify Black Rock w/ Green Flecks
« Reply #13 on: 21/11/2012 17:41:21 »

 

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