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Author Topic: Need Your Help! I don't know what these rocks are...  (Read 14234 times)

Offline redm

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Hi! I wonder if you knowledgeable folks can help me identify these rocks. I really don't know what they are so I won't be able to tell you if you are right or not. I can't tell you where they came from either-other than they are part of a mixed lot acquired by a freight recovery company.

Here's the first one (coke can is in the picture to show the relative size):



Many thanks to all who answer!


 

Offline Karen W.

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Need Your Help! I don't know what these rocks are...
« Reply #1 on: 02/02/2008 20:28:35 »
Looks like a fossil of a daisey like flower or some such flower..perhaps a zinnia..

The rock looks as if it once had flowed perhaps it is some kind of volcanic rock? I am not a Geologist , one will come soon to this post .. in the mean time how cool is that.. Very cool rock!
 

Offline redm

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Need Your Help! I don't know what these rocks are...
« Reply #2 on: 02/02/2008 20:45:47 »
Thank you, Karen. I don't know any more about fossils than I do about rocks, although the white appears to be a growth rather than an indentation.

Here is a close-up:

 

Offline Karen W.

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Need Your Help! I don't know what these rocks are...
« Reply #3 on: 02/02/2008 20:54:56 »
Kinda quartz looking on that white part , but what a unusual pattern of quartz formation if it is.. very interesting and the closeup looks great!
 

Offline JimBob

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« Reply #4 on: 02/02/2008 21:31:59 »
Where did it come from and how hard is it - in relationship to other rocks? Is the angular black thing it is coming out of a piece of black shale?
 

Offline redm

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Need Your Help! I don't know what these rocks are...
« Reply #5 on: 02/02/2008 22:13:54 »
I don't know where it came from. I understand that this piece was broken off from a larger piece, but the larger piece was primarily the black. I don't know if it is shale, but the black isn't oily. The white and black seem to be of about the same hardness...now what to compare it to...it's pretty hard, I couldn't scratch it with my fingernail, I think it would probably take a knife or nail to scratch it. I don't know but suspect it is harder than quartz. When I get back to work (where it currently resides)I'll try scratching it with some amethyst and see what happens.

Any idea on how to describe the "flower" formation?
 

Offline redm

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Need Your Help! I don't know what these rocks are...
« Reply #6 on: 02/02/2008 22:18:54 »
Here's another one, which I suspect may be easier. It's layered and flaky, shiny and pinkish. It's a lot prettier than the pictures.


 

Offline Bass

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Need Your Help! I don't know what these rocks are...
« Reply #7 on: 03/02/2008 00:28:43 »
The bottom rock is schist.  (Not the kind that grows daffodils, Neil).  Biotite schist, to be more specific- which is a metamorphic rock with prominent biotite (black mica) layering.  This specimen is bordering on gneiss (pronounced "nice")

Upper specimen is probably black shale with gypysum crystals forming a "rose"  Gypsum roses are not uncommon, especially in caves- but I haven't seen many that size.  Possibly could be calcite instead of gypsum.
 

Offline redm

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Need Your Help! I don't know what these rocks are...
« Reply #8 on: 03/02/2008 03:31:43 »
Wonderful, Bass, thank you!

Here's another:



 

Offline redm

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« Reply #9 on: 03/02/2008 03:57:01 »
One more before the cold medicine claims me for the night (I thought the dark grey looked alot like the some of the pyrite I've seen):




 

Offline JimBob

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« Reply #10 on: 03/02/2008 05:02:57 »
The top rock is a the result of a series of events. First the grey rock was depositeed. Then the black rock broke it apart, either by being injected as an igneous rock or slowly growing by water passing though small cracks breaking the grey rock apart. THEN the whole mass was broken apart. It became a small boulder. Eventually, it got rolled around in water but not for very long because the black rock still has jagged edges. The black stuff came apart as seen in the close-up picture and it was in the mud or carbonate matrix as a result of probable mechanical action.

This looks like rocks I have seen in alluvial fans and deep water conglomerates from the Tesnus Formation in west Texas. But the Tesnus is a much less probable origin for this. It was probably found in an alluvuial fan on the side of a mountain range somehwere.

Bass is going to need to speculate on the second. It looks like lead with some hydrothermal roses growing on it BUT there is a an inclusion of a foreign rock in it. My best guess would be part of a volcanic "bomb" a piece of lava formed in a a volcano vent ans then ejected after a period of growth by gases from the volcano as it is erupting.   

Bass is a "hard rocker" and I am a "soft rocker" (no, not rock band type). This means Bass specializes in minerals, igneous and metamorphic rocks and I specialize in sedimentary rocks.

We are a hard team to beat. But then Bass gripes a lot because he is old. I quote from the gyser subject "I'm gone two weeks and look at the mess I have to clean up!  (That'll teach me for leaving)" He is referring to the mess I made but I just shrug this off as I know this is the beginning of dementia. My heart goes out to the poor man.





 

Offline Bass

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« Reply #11 on: 03/02/2008 20:12:34 »

Bass is a "hard rocker" and I am a "soft rocker" (no, not rock band type). This means Bass specializes in minerals, igneous and metamorphic rocks and I specialize in sedimentary rocks.

We are a hard team to beat. But then Bass gripes a lot because he is old. I quote from the gyser subject "I'm gone two weeks and look at the mess I have to clean up!  (That'll teach me for leaving)" He is referring to the mess I made but I just shrug this off as I know this is the beginning of dementia. My heart goes out to the poor man.

I have to agree with JimBob (a first, no doubt), our geological backgrounds do make for a good team, despite the occaisional ribbing we give each other.  As to his quip about my dementia.... oh sorry,  what we were chatting about??? ??? ???

Put 10 geologists in a room and hand them a rock specimen; and you'll end up with 10 different opinions on what the rock is and how it formed- but then again, that's the fun of the science.  (I'll bet JimBob's x-ray vision is still no better than mine)

As such, I respectfully disagree with some of JimBob's interpretations on the top rock.  I agree that the grey rock was the first deposited- but this was then brecciated (broken into fragments).  The black material (possibly metallic sulfides, tourmaline or carbonaceous minerals) was emplaced as open-space filling by hydrothermal fluids (hot waters).  Notice the rounded nature of the breccia fragments, especially along the right hand side of the specimen- suggesting absorption/replacement by the black material during hydrothermal mineralization.

The brown surrounding the grey/black rock is probably due to weathering (iron oxides).  After fragmentation and hydrothermal minerals, this specimen was overlain by a thin white layer, then more of the grey rock.  The top of the rock may have casts of woody reeds/stems- common in hot spring environments.

redm, could you please wet down the rock and retake photos- this will allow us to see through some of the saw marks.  Also, please photograph the side with with the orange sticker.  Thanks.

JimBob nailed the second specimen.  Probably galena- lead sulfide- surrounded by sulfate crystals (possibly anglesite).  Judging from the look, the metallic mineral might also be tetrahedrite or tennantite.  The sulphates probably form using sulfur in the galena or in the hydrothermal solutions- but they had to form in open space!  (otherwise, the delicate crystals could not form).  Sulphates are very common in hydrothermal mineral systems- this probably formed in some sort of fracture above a cooling granitic pluton.  I don't see JimBob's inclusion??  Very nice specimen.

photo of tennantite (black) with sulphate minerals (white)

 

Offline JimBob

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« Reply #12 on: 03/02/2008 23:22:44 »


Circled - isn't that an inclusion?

As for the first rock I think it is sedimentary but I also said "Then the black rock broke it apart, either by being injected as an igneous rock or slowly growing by water passing though small cracks breaking the grey rock apart" Hydrothermal water is still water and I intended it to be part of the process. Minor quibble.

What makes me think the grey rock is sedimentary is that it has two layers, best seen on the left side of the top picture along the long fracture running left to right and marked by arrows where the grey turns to tan and has a layer of darker tan rock on top. The black is quite possibly a black carbonate as I have seen this in the Austin Chalk. The host rock (the big thing, is also sedimentary because of the fossils or trace fossils on it and the layering that also penetrates to the rock underneath. See arrows



The fossils are what look to be straight ammonites or worm tracks but may be just marks made by mechanical action as one seems to connect to the grey fracture fill indicated by the left-most upper arrow.

Since the black fills more rocks than the grey-tan, but also the bottom brown layer, I think it must have been deposited after the grey was in the bottom brown layer.
« Last Edit: 03/02/2008 23:29:02 by JimBob »
 

Offline Bass

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« Reply #13 on: 03/02/2008 23:52:36 »
I took your inclusion to just be thin sulfates on the surface- but perhaps you are right.  Hard to tell from the picture.

I agree that the grey rock is probably sedimentary, the black is obviously open-space filling along fratures, especially when you see stripes parallel to fracture walls. 
Intersting that the black mineral does not appear to penetrate the upper two layers.
I still think the outer brown layer surrounding the brecciated rock is from oxidation of the black mineral- which, if true, would suggest the black mineral contains sulfides, probably pyrite.  Note the black mineral on the upper right side of the photo and along the length of the brown (in the middle) just below your right-most arrow. But brown could also be siderite if this specimen is all carbonate?
« Last Edit: 03/02/2008 23:56:43 by Bass »
 

Offline redm

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Need Your Help! I don't know what these rocks are...
« Reply #14 on: 04/02/2008 00:20:27 »
Well, this is fascinating. Obviously this is not knowledge that you can just pick up in a few hours of searching the internet in a bumbling way--which is what I've been doing.

Thank you very much for your help. I'll try to get a picture of the top rock wet.

Here's a couple more (the top one has amethyst color in it, the dull area on the second one is just where a label was removed):





 

Offline Bass

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« Reply #15 on: 04/02/2008 00:35:01 »
bottom photo is petrified wood.

top photo???  Can you scratch it with a knife or nail?  Penny?  Possibly massive flourite.
 

Offline JimBob

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« Reply #16 on: 04/02/2008 01:36:57 »
Au contraire, mon ami - the bottom could possible be tiger's eye agate. It is banded and fibrous. How expensive was this rock, redm? I suspect Bass is correct, though.

Lepidolite & Spodumene could also be possibilities, spodumene more likely since the rock is not vitreous in luster and the specimen looks as if it could be a hydrothermally deposited rock - see contact on the bottom.

These are just suggestions.
 

Offline redm

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« Reply #17 on: 04/02/2008 02:17:32 »
I'll do some testing at work with scratching, but my guess is that a penny could scratch the purple one. The brown one didn't have a price tag, just one of our inventory labels--which I removed, albeit not completely :( for the picture.
 

Offline JimBob

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« Reply #18 on: 04/02/2008 02:39:32 »
Hey - free consulting? Hum, Bass, do you think we need to bill him?

 ::)
 

Offline Bass

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« Reply #19 on: 04/02/2008 04:08:38 »
Hey - free consulting? Hum, Bass, do you think we need to bill him?

 ::)

What's the old addage..."You get what you pay for"?

Consulting fee, eh?  Let's see, why don't we start with minimum wage, multiplied by the combined ages of the consultants (this could get expensive), add a splash of oil and a gold nugget and voila... nobody can afford our services!

redm- if the rock is really soft, could be erythrite (hydrous cobalt arsenate)- but erythrite is rare and usually found in contact with cobalt minerals.  More likely is rhodochrosite (manganese carbonate) which is close to the hardness of a penny. (use an old penny, new ones are made of zinc)

I will be leaving for at least 10 days in the morning, but will try to check back here again later tonight.
 

Offline JimBob

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« Reply #20 on: 04/02/2008 16:24:53 »
Isn't rhodochrosite bright pink?
 

Offline opus

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« Reply #21 on: 04/02/2008 19:21:37 »
You guys really know your rocks- fascinating- I'm still very much a learner- but I think they're great.
 

Offline Bass

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« Reply #22 on: 04/02/2008 20:10:14 »
Isn't rhodochrosite bright pink?

Unlucky travel day, highway closed due to avalanches- will try again tomorrow.

gem quality rhodochrosite is usually pink, but the mineral can vary from pink to blood red to purple.  rhodochrosite from Mn mines near Philipsburg, MT is deep violet color.
 

Offline JimBob

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« Reply #23 on: 05/02/2008 00:17:17 »
Isn't Mn what makes Lepidolite purple as well?
 

Offline Bass

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« Reply #24 on: 05/02/2008 00:33:14 »
Flourine, I think, adds the purple color.  Purple in photo doesn't appear to be micaceous which is why I didn't consider lepidolite.
 

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Need Your Help! I don't know what these rocks are...
« Reply #24 on: 05/02/2008 00:33:14 »

 

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