Possible kimberlite, lamproite, or rhyolite, or.....

[Jim in Idaho]

The wife and I found this last weekend while crusing some rough country in northern Nevada, It was lying next to a two-track, and I spotted the greenish cast as we drove by. The rock in that country is almost all dark brown, or dark reddish brown, either basalt, or rhyolite lava. This rock was a definite an anomaly. I don't know if there was an outcropping that got hooked by the blade of the patrol, or if the rock was hauled in from somewhere else. Didn't have time to do much looking around. Probably won't get back there until spring. If any of you guys, or gals has an idea, please post up.
Thanks, Jim

 

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[rodoconnor]

Cool Jim. Go find some Nev diamonds !

 

[Eu_citzen]

Ohh, now that's a tricky bugger. Do you see any quartz under magnification? Can't tell for sure from the pics.

 

[Jim in Idaho]

No way to tell by appearance. There are whitish materials, but some of it is snow white, some looks like quartz, but could be other minerals. I put muriatic acid on it, with no reaction I could see. No distinct odor on a newly broken face. I did get some fluoresence in a couple of spots...probably calcite. What I need is a simple test for potassium.
Jim

 

[BurntBear]

Haven't seen anything quite like that. Interesting specimen!

 

[Eu_citzen]

Well, the colour looks mafic, possibly basalt or a relative to that group? I haven't seen kimberlite to often and it never looked like that. It never had any "grains" of other minerals in it.
Though as I said, I only ever saw it a few times and I could be totally wrong.

I remember it is soft though, very soft. (due to mica content?) Try scratching it with a knife. Kimberlite often is altered to serpentine-related minerals and carbonates to.
Also, due to the softness kimberlite will often form lakes, and other "roundish" depressions. Look at maps, they often occur in groups.

 

[Jim in Idaho]

Well, the colour looks mafic, possibly basalt or a relative to that group? I haven't seen kimberlite to often and it never looked like that. It never had any "grains" of other minerals in it.
Though as I said, I only ever saw it a few times and I could be totally wrong.

I remember it is soft though, very soft. (due to mica content?) Try scratching it with a knife. Kimberlite often is altered to serpentine-related minerals and carbonates to.
Also, due to the softness kimberlite will often form lakes, and other "roundish" depressions. Look at maps, they often occur in groups.

Yup...I've been prospecting for diamonds for a couple of years, so know a little on kimberlites. I'm fairly sure it isn't. No chrome diopside, no garnets. I'm thinking it's either a form of rhyolite, or it's a lamproite ( I hope...LOL). Though I've never seen a rhyolite that had any green in the color. This rock, at least to my eyes, has a distinct greenish shade to it....especially on the freshly broken faces. This rock is also hard, though a freshly-broken face can be scratched with a knife blade. The rock definitely has some K-feldspar in it....which doesn't really tell us much.
I've examined the area carefully on Google Earth. No anomalies stand out. I did see one patch of lighter-colored soil a couple of miles up the drainage from where I found the rock.....that will need looking at next spring.
Jim

 

[Buckshotnc]

Here in Western North Carolina at my farm I have some ultramafic deposits which the geologists tell me in perioditite/lamproite possibly dunite which has a mostly green interior even though the exterior may be weathered to an almost grey. There is also yellow mica and mostly green inside unless it has deteriorated or retrograded to a mostly black and brownish color. The green being primarily olivine. Your rock seems somewhat similar except for the black patches in it. Your reddish color could be iron or corundum. I'm sure there are others on here who know more than I geologically speaking, hope they will help you more. I will say that there have been diamonds found in the stream that flows through my property by the old time 1800-1900 gold prospectors, most locations were not specifically identified except for one or two locations down stream, one being the largest diamond ever found in NC which was 4.3 carats. You never know so keep looking with an open mind, you never know !

 

[Jim in Idaho]

Thanks, Buck....I'm definitely going to be prospecting that area. I'm thinking I may have found a lamproite pipe. If so, I think it's the first in Nevada, which is pretty interesting. I doubt I'll get back down there this fall, but we'll see. Of course, I'll keep everybody posted on how things go.
Jim

 

[Eu_citzen]

Yup...I've been prospecting for diamonds for a couple of years, so know a little on kimberlites. I'm fairly sure it isn't. No chrome diopside, no garnets. I'm thinking it's either a form of rhyolite, or it's a lamproite ( I hope...LOL). Though I've never seen a rhyolite that had any green in the color. This rock, at least to my eyes, has a distinct greenish shade to it....especially on the freshly broken faces. This rock is also hard, though a freshly-broken face can be scratched with a knife blade. The rock definitely has some K-feldspar in it....which doesn't really tell us much.
I've examined the area carefully on Google Earth. No anomalies stand out. I did see one patch of lighter-colored soil a couple of miles up the drainage from where I found the rock.....that will need looking at next spring.
Jim

I've been wondering if a weathered diabase should be a prime suspect. But that you can scratch it with a knife would rule that out to.
Call it, "greenstone". A book called "Rocks and Rock Minerals" could help you ID some of your finds, a really useful resource. I forgot who wrote it, though.

 

[Jim in Idaho]

From people I've communicated with, it's starting to look like it's either rhyolite tuff, or lamproite tuff. It's probably been re-sedimented, or possibly the residual heat has caused some of the other rocks to be fused in place (like the dark one). I think it's definitely got peridotite in the matrix, so there's a possibility of it being lamproite. That means there could be diamonds, but the odds are still really low. Definitely worth a few days prospecting, though. I'm currently installing an 8" steel pipe chimney in the shop, previous to the installation of a woodstove, so don't have time to go back, this week. If the weather holds, I may get back there this fall.
Jim

 

[rrhobdy]

Hi Jim...

I can tell you what it's not... It definitely is not kimberlite, lamproite, lamprophyre, or peridotite. Your pic nr. 4 told the story. It is piece of rock from a quartz vein, with mica and rusted out areas from pyrite. About midway up right side, you can see drusy quartz, and center right, you can see quartz cementing other elements. The green color is probably imparted from copper family, probably a chlorate or sulfide. I would look for a vein in the nearby country rock, probably along a fault line, which would explain the broken bits cemented together by quartz or silica minerals. This would be normal if you are in an area with some volcanics nearby, or igneous/metamorphic contact zone.

Bob

 

[Jim in Idaho]

Many thanks, Bob. I'll be poking around that area come spring. I still plan on crushing a piece of this and seeing what comes of that.
Jim

 

[Ddiamond Digger]

Hi Jim,
Hope this helps!
See you in the Badlands!
Andy



Lamphorite


Kimberlite from my one site

outcropping

 

[Jim in Idaho]

Hi Jim,
Hope this helps!
See you in the Badlands!
Andy


View attachment 1710894
Lamphorite

View attachment 1710895
Kimberlite from my one site

outcropping

LOL...this is an old thread, Andy, but you DO find some great stuff! Heidi and I are looking forward to seeing you this summer.
Jim