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Author Topic: What can you tell me about these stones ?  (Read 11888 times)

Offline neilep

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What can you tell me about these stones ?
« on: 28/03/2006 16:46:06 »


 Note the cloudy glassy cut-a-way...what's that ?



 What are those blobby things ? ...and No, they're not chewing gum !!


I was in the garden just now and picked this stone up...can someone please tell me a bit about it, especially what the cloudy almost glassy facet is composed of.  Bass ? Ophioliote ? G1 ? Exodus ?...

How old could this stone be ?

Oh, By the way...this is not a test...I don't know and am genuinely interested.

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« Last Edit: 29/03/2006 03:58:43 by neilep »


 

Offline daveshorts

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Re: What can you tell me about these stones ?
« Reply #1 on: 28/03/2006 17:29:31 »
Looks like a fairly low quality flint to me... you live in london right? Flint is often found in chalk, and most of the chalk in the uk is Cretaceous... so at the youngest 65million years.

some microscopic creatures make shells out of silica rather than the calcium carbonate that makes up most of the chalk. This dissolves and then gets redeposited in a nodule - I think a lecturer once said it tended to be where there was some organic matter which made the area more acid. The lumpy bits on the outside are where the module meets the chalk, I am not too sure of exactly what they are.

The resulting flint behaves like a glass, and when broken will make a very sharp edge, hence prehistoric man's fondness for it. I am not sure he would be keen on your's though neal, the good stuff tends to have much smaller crystals.
 

Offline neilep

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Re: What can you tell me about these stones ?
« Reply #2 on: 28/03/2006 18:35:51 »
Thanks Dave, (sorry I omitted you off my list in the original post )

Yep, I'm in North London. I appreciate your insight into my economy class flint !!  ;)

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Offline Bass

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Re: What can you tell me about these stones ?
« Reply #3 on: 28/03/2006 20:06:03 »
Hi Neil

Great rock smiley face in the bottom pic!

Dave may be right- looks like flint.  Also possible that this may be quartz or chalcedony (actually, flint, quartz and chalcedony are basically the same thing).  The fact that it is round (no angular sides) suggests mechanical weathering- as in a streambed.  Are round stones common in your garden?

"Blobby things"- no wonder I can't keep up with the technical jargon in the earth sciences:D
Looks more like this stone is coated with some material, and the blobby things are where the coating has broken off.  I can see a rust stain on the top picture, possibly you bent your shovel when you hit this stone while planting rutabaga?  Anyway, the iron stain suggests that the stone is hard.  As to the coating- try dripping a bit of dilute hydrochloric acid on it and see if fizzes- if so it is calcium carbonate.
Then again, maybe this is a fossilized tyrannosaurus (or pick your favorite dinosaur) egg?  The lighter shading in the top picture resembles an early fetus.
Age?  Probably older than the Norman conquest.  Dave's Cretaceous age is as good a guess as any.

Subduction causes orogeny.
« Last Edit: 28/03/2006 20:06:46 by Bass »
 

Offline neilep

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Re: What can you tell me about these stones ?
« Reply #4 on: 28/03/2006 20:27:23 »
Thanks Skip,

I certainly wasn't planting rutabaga, though I do love it !!(after looking it up to see what it is, and I'm not going to say what it is so that others can look it up too !!)

Glad you like the technical term 'blobby...as you know I am very cerebral on this site :D and I do hope that my use of terms didn't daunt you too much.

I think you're right, it's either a cavemans early smiley or indeed a T Rex egg; and as a firm believer in empirical study I will let wifey sit on it when she's on the telephone !..because like most girlies on the phone, she speaks at length.:D

Seriously though, I thank you and Dave for your diagnosis. I realise it also tricky because it's just a photo but your explanations are fascinating.

THANK YOU.

I may post others if that's Ok.. I have lots of interesting stones in my garden.

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Offline daveshorts

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Re: What can you tell me about these stones ?
« Reply #5 on: 28/03/2006 23:01:46 »
Just one thing, flints come out of the chalk nicely rounded like this so it doesn't have to have been in a stream.
 

Offline JimBob

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Re: What can you tell me about these stones ?
« Reply #6 on: 29/03/2006 01:57:48 »
Neil,

It's low quality flint, alright. But the "blobby things" in this one only appear to be calcite filled burrows, esp. the nearly straight one on the right, pionting up to the left, that is also most likely the round slightly darker cream-coloured object on the surface just to the right of the broken surface.(I spelled coloured just the way you like it - I realize how hard reading is for you.)

These do not need to be formed in a void space in the chalk. They are formed as loosely consolodate sediments compact into rock. That this particular flint nodule has "burrows" is just accidental. If they are burows it is a little unusual but not unknow. I have picked up some in the field from the Upper Cretacoeus Austin Chalk that have the same features. In the ones I have handled, the burrow-filling was softer than both the nodule proper and on the coating, the transition zone between the chalky matrix and the contained silicous flint.

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« Last Edit: 29/03/2006 02:01:55 by JimBob »
 

Offline neilep

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Re: What can you tell me about these stones ?
« Reply #7 on: 29/03/2006 02:38:11 »
Thank you too JimBob.


All this wonderful information you have all given me has made me feel quite attached to this stone now. I've even begun to anthropomorphise it ! It would make a great papeweight and feels good in the hand.

Jim, what would have created the burrow ?...a worm on steriods ?


I do in fact have some really really old fossils too..I'll have to post them here for all your wonderful deliberations and examination.
 

Offline JimBob

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Re: What can you tell me about these stones ?
« Reply #8 on: 29/03/2006 03:08:56 »
No steroids needed. All sorts of things make burrows, worms, shrimp gastropods, fish. Pick your poison.  Rememnber, the burrows were made when the carbonates were soft. The silica didn't replace the burrows, if this is what they indead are.

How about Mergetroid?

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Offline neilep

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Re: What can you tell me about these stones ?
« Reply #9 on: 29/03/2006 03:49:11 »



...and this one...?...is this ancient in the extreme ?

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Offline JimBob

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Re: What can you tell me about these stones ?
« Reply #10 on: 29/03/2006 06:05:03 »
Ever had scallops in marinara sauce? Well, this is what your looking at. It is an ancient scallop or to use "jargon," a Pectin, one of the numerous of the family Pectinidae. (The part you eat is the one big muscle that holds the shell together. I know some DNA guy has probably  wiped this family off the map - invertabrate taxonomy has changed since my textbook by Moore, Lalliker and Fisher, written in the dark ages.)

I think they are known as cockles in The UK.

They have been around for a long time. I am not sure how long but (I'm trying to remember) possibly the Paleozoic - Permian or before. But if corrected by someone, the Triassic, ~250 Ma.

If it helps, these shells are the logo for Royal Dutch Shell.

There are also two or three things the look like squashed "Q's" in the rock, the biggest one just below the pectin, and at least one more smaller one shy of the upper edge on the left side as well. Can you get a close-up of the big one? I might be able to tell you what it is but no guaranties. I am not a paleontologist.

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Offline Bass

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Re: What can you tell me about these stones ?
« Reply #11 on: 29/03/2006 06:54:31 »
Neil- you dog!  How long did it take you to chisel out that seashell shape?  Or maybe you just painted it on?:D

I have to defer to Jim's soft-rock experience here.  I'm an old, hard-headed hard-rocker- which means I don't see alot of well-preserved seashells in the rocks I deal with (though sometimes I get to play with the sedimentary rocks around skarns).  Don't you have any igneous or high-grade metamorphic stones in your garden?

Subduction causes orogeny.
 

Offline Ophiolite

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Re: What can you tell me about these stones ?
« Reply #12 on: 29/03/2006 08:32:17 »
quote:
Originally posted by Bass

I'm an old, hard-headed hard-rocker-
I take it that you view anything Cambrian and later as superficial drift deposits.;)

Observe; collate; conjecture; analyse; hypothesise; test; validate; theorise. Repeat until complete.
 

Offline neilep

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Re: What can you tell me about these stones ?
« Reply #13 on: 29/03/2006 15:23:32 »
Originally posted by Bass
quote:

Neil- you dog!  How long did it take you to chisel out that seashell shape?  Or maybe you just painted it on?:D


...oooh..about half an hour ![:D]



 
quote:
Don't you have any igneous or high-grade metamorphic stones in your garden?


I beg your pardon ? :D

JimBob,

It's difficult to get a close up, I'm using a four year old 4Mega Pixel digital camera, one of the best in it's day but now quite antiquated...almost a fossill in itself !!

I have tried to get a closer picture.!



PICTURE 1



What about these ?



PICTURE 2



PICTURE 3...the Other Side !


THANK YOU....there's more !!





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« Last Edit: 29/03/2006 15:38:45 by neilep »
 

Offline JimBob

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Re: What can you tell me about these stones ?
« Reply #14 on: 29/03/2006 15:50:51 »
quote:
Originally posted by Ophiolite


quote:
Originally posted by Bass

I'm an old, hard-headed hard-rocker-
I take it that you view anything Cambrian and later as superficial drift deposits.;)




Yeh, Bass probably calls it overburden. That includes houses, streets, cars, people - get it out of the way so we can get to the ore!

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Offline JimBob

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Re: What can you tell me about these stones ?
« Reply #15 on: 29/03/2006 16:25:08 »
About the limestone (with pectin) I can't tell what those things are for sure. The upper one, with the oblique lighting, may have been a place where a broken piece of pectin shell was pressed into the mud and the shell fell out. The one below the pectin is less certain.

BUT the new lighting angle lets you see the tracks of a (probable) worm, the small fillagree paths on the top surface. These are (hold your nose) the fossilized excrement of the worms(?) as they work their way through the surface of the sea floor taking in everything on the bottom of it, passing the mud and nutrients through their gut to get the food out, then leaving a long "log" as they eat. Nice table manners, eh?

A piece of fossilised s**t is called a coprolite. So the next time someone gives you a bad time and you want to insult them yet do not want them to know, call them a coporolitic, maladroit (substitute suitable noun). Use it for the snotty ones.

As for the black rock, it is a black rock.

Shale (with some trace fossils?) It may have been slightly metamorphosed into slate - Bass?


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Offline Bass

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Re: What can you tell me about these stones ?
« Reply #16 on: 29/03/2006 17:07:29 »
quote:
Yeh, Bass probably calls it overburden. That includes houses, streets, cars, people - get it out of the way so we can get to the ore!
Hey, I resemble that remark!
 
quote:
...a coporolitic, maladroit (substitute suitable noun)...
And that one!


Jim has it right- black rock, looks only slightly metamorphosed.  The very minor sheen is probably due to the formation of mica minerals replacing the clay.  Does your finger turn black when you rub the rock?  If so, it may indicate the formation of graphite, which is common in slightly metamorphosed rock.

Subduction causes orogeny.
 

Offline neilep

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Re: What can you tell me about these stones ?
« Reply #17 on: 29/03/2006 17:59:54 »
THANK YOU JIMBOB & BASS

what about this one ?...I hope you don't mind...it's a crystal yes ? quartz ?...age ?





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Offline Ophiolite

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Re: What can you tell me about these stones ?
« Reply #18 on: 29/03/2006 18:57:42 »
The black rock is, as has already been noted, a shale. I don't think it is metamorphosed, just well indurated. Of course the division between intense diagenesis (the changes that take place to a sediment that turn it into a rock) and metamorphism are somewhat arbritary.
It is deinitely carbonaceous, and those trace fossils look more like plant fragments to me, but I'm no palaeobotanist.


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Offline daveshorts

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Re: What can you tell me about these stones ?
« Reply #19 on: 29/03/2006 19:23:37 »
I am not sure why I think this but it looks mor like calcite (recrystalized limestone) than quartz, is it harder than mild steel? if so it is probably quartz. If it is either calcite or quartz, I don't think you can date it visually except from the surrounding rocks, as it is formed by dissolving and recrystalizing another rock, so it is too pure for much in the way of aging details to be preserved..
 

Offline JimBob

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Re: What can you tell me about these stones ?
« Reply #20 on: 29/03/2006 19:36:59 »
Damn! Feel as if I am doing my Geology 101 (physical geology) Lab final all over again. I think across the pond it is called sitting for the orals with a specific lecturer.

If it has six sides, it's quartz. Beta-Quartz, to be exact. There is a yellow orthorhombic (pseudohexagonal) mineral OCCASIONALLY mistaken for quartz - topaz. I highly doubt your that lucky!

(poke you in the eye :D)

The reason is that there is a lot of iron stain. It would be green or red if the iron were substituted for the aluminum in topaz crystal structure.

Interesting little fact, there is a rock mined for building finishing here in Texas named Llanorite. It is casually called a granite (formed underground) but is actually a rhyolite (same mineral composition - volcanic origin).  It has one of the few occurences of alpha-quartz I  know of. Because of the difference in the quarts crystal the alpha-quartz is bright blue.

I would send a picture if my digital camera were working.

BASS, OPHIOLITE, DAVE - JUMP IN - I do not want to hog this thing. Neil, to let them have a chance to pontificate instead of me holding forth, I will defer to them for several of your pictures.


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Offline neilep

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Re: What can you tell me about these stones ?
« Reply #21 on: 29/03/2006 20:15:59 »
quote:
Originally posted by JimBob


I would send a picture if my digital camera were working.

BASS, OPHIOLITE, DAVE - JUMP IN - I do not want to hog this thing. Neil, to let them have a chance to pontificate instead of me holding forth, I will defer to them for several of your pictures.


The mind is like a parachute. It works best when open.  -- A. Einstein



Jim, my camera is working, just send me a first class return ticket to where you live and I'll lend you it !

Glad I could help :D

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Offline Hadrian

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Re: What can you tell me about these stones ?
« Reply #22 on: 05/04/2006 18:53:27 »
just send me the stones and i photograph them for you .sometime! :D:D:D

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Re: What can you tell me about these stones ?
« Reply #22 on: 05/04/2006 18:53:27 »

 

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