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mickiver

Could Be An Egg.......

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JohnJ

....So, mineral nodule/concretion looks most likely....

Additional images will help.

Roger, I use "pebble" rather broadly; I thought we were in close agreement. ;)

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Mr_ed

I have larger concretions that have been stream polished that look like that but they are not any lighter than rock.. maybe heavier. I also have concretions that are pretty much round and about that size that are not stream polished .... and are grey in color. It strongly resembles a concretion that has been stream polished. It doesn't appear to be shinny or smooth enough surface to be pearl .. comparing pictures anyway..

Edited by Mr_ed

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Herb

looks almost like hematite?

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painshill

looks almost like hematite?

Yes it does, which would be consistent with a Moqui-type concretion... but it would have to be hollow. A streak test would tell us more.

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mickiver

I feel like Capt Jack Sparrow, I've lost the black pearl.

Weight = 32.6g, Volume = 12.5ml, Specific Gravity = 2.608

A short search led me to Steatite, aka soapstone.

From "Soapstone" by Edward W. Parker:

Occurrence.

Soapstone or talc is found in nearly every State along the Atlantic Slope, the principal deposits being in New York and North Carolina, though it is also quarried in New Hampshire, Vermont, Massachusetts, New York, New Jersey, Pennsylvania, Maryland, Virginia, North Carolina, and Georgia. It has also been reported in some of the Western States, particularly in California, Arizona, South Dakota, and Texas, but no commercial product has been obtained west of the Mississippi River. Pure soapstone is a massive amorphous mineral, usually white, light green, or gray in color. In some cases, notably at Gouverneur, St. Lawrence County, N. Y., it occurs in a foliated or fibrous form, very valuable as a filler or makeweight in the manufacture of paper. This latter variety, known as fibrous talc or mineral pulp, is considered separately these reports.

The first four pictures are of a pre-columbian bead found in California made from soapstone.

It is also known as a wiskey stone as it can be frozen and added to a drink to keep it cold without diluting it.

post-12514-0-98101100-1374714963_thumb.jpg

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post-12514-0-30161400-1374715349_thumb.jpg

post-12514-0-50454900-1374715351_thumb.jpg

post-12514-0-73526800-1374715353_thumb.jpg

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Indy

I feel like Capt Jack Sparrow, I've lost the black pearl.

Reminds me of ...

The Curse of the Black Pearl

:P

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Roadrunner

Can't soapstone be scratched with a knife? I thought it had varying levels of talc.

Edited by Roadrunner

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PA Fossil Finder

Most soapstone, as far as I know, can be carved with a knife.

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Roadrunner

Most soapstone, as far as I know, can be carved with a knife.

I understand the talc in it can vary from 30-80%.

Even at 30% a knife should be able to cut it.

I'm not sure what happens to it if/when it becomes fossilized, however.

Edited by Roadrunner

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AgrilusHunter

I'm not sure what happens to it if/when it becomes fossilized, however.

Well, if I remember right, soapstone is a type of schist so it's already been metamorphosed. Soapstone with lower (30%) amounts of talc is actually pretty hard and is even used for counter tops and sinks. I imagine you could still scratch it with a knife pretty easily though.

Edited by AgrilusHunter

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painshill

A few observations.

I based my (somewhat premature) estimate of a density of 1.9g/cc on the diameter I could see against the ruler in the first pictures and approximated that to a sphere. Unless the perspective belies that diameter, for a measured density of 2.6g/cc then the item must deviate rather more significantly from spherical than the pistures show (as noted by Auspex). The density is then easily within range for many common igneous and metamorphic rocks. Granite for example (not suggesting it is granite) is around 2.6-2.7g/cc.

As AgrilusHunter says, soapstone (steatite) is a metamorphic rock which comes in a range of hardness values, starting with material so soft that it can be scratched with your fingernail. But if it has a hardness beyond 5.5 (cannot be scratched with a penknife blade) then it isn’t soapstone. Generally, only end members of the group such as Enstatite or Cristobalite have higher hardness values (up to about 6.5).

Although soapstone talc has a density of around 2.4g/cc, it’s extremely soft. Soapstone itself is a moderately dense rock – typically around 3g/cc – and it’s that density which makes it suitable for kitchen worktops since it doesn’t stain and bacteria don’t penetrate the surface. Soapstone also has good thermal conductivity and a high specific heat capacity - hence its use for “whiskey stones” (and also its use for heating stones used in Native American times).

Other things you might like to check… because of its thermal properties, soapstone doesn’t normally feel cold to the touch (hold it against your cheek) and typically has a “greasy” feel to it. The darker harder varieties with lower talc content almost always have tiny inclusions of ferrous material in them such that they are often weakly magnetic (even with an ordinary magnet rather than a rare-earth one).

It might look like soapstone (why are we so focussed on how it looks?) but it doesn’t have the typical properties to support that. If we are now talking about a smooth, shiny, black rock with a partial/semi-crystalline nature which is approximately round, fairly hard and has a density of 2.6g/cc then there are literally dozens of things it could be and I would question if there is any particular reason to regard it as anything more exotic than a water-polished pebble (as noted by JohnJ).

Edited by painshill

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Mr_ed

A few observations.

I based my (somewhat premature) estimate of a density of 1.9g/cc on the diameter I could see against the ruler in the first pictures and approximated that to a sphere. Unless the perspective belies that diameter, for a measured density of 2.6g/cc then the item must deviate rather more significantly from spherical than the pistures show (as noted by Auspex). The density is then easily within range for many common igneous and metamorphic rocks. Granite for example (not suggesting it is granite) is around 2.6-2.7g/cc.

As AgrilusHunter says, soapstone (steatite) is a metamorphic rock which comes in a range of hardness values, starting with material so soft that it can be scratched with your fingernail. But if it has a hardness beyond 5.5 (cannot be scratched with a penknife blade) then it isn’t soapstone. Generally, only end members of the group such as Enstatite or Cristobalite have higher hardness values (up to about 6.5).

Although soapstone talc has a density of around 2.4g/cc, it’s extremely soft. Soapstone itself is a moderately dense rock – typically around 3g/cc – and it’s that density which makes it suitable for kitchen worktops since it doesn’t stain and bacteria don’t penetrate the surface. Soapstone also has good thermal conductivity and a high specific heat capacity - hence its use for “whiskey stones” (and also its use for heating stones used in Native American times).

Other things you might like to check… because of its thermal properties, soapstone doesn’t normally feel cold to the touch (hold it against your cheek) and typically has a “greasy” feel to it. The darker harder varieties with lower talc content almost always have tiny inclusions of ferrous material in them such that they are often weakly magnetic (even with an ordinary magnet rather than a rare-earth one).

It might look like soapstone (why are we so focussed on how it looks?) but it doesn’t have the typical properties to support that. If we are now talking about a smooth, shiny, black rock with a partial/semi-crystalline nature which is approximately round, fairly hard and has a density of 2.6g/cc then there are literally dozens of things it could be and I would question if there is any particular reason to regard it as anything more exotic than a water-polished pebble (as noted by JohnJ).

I certainly don't disagree with you but I have to ask.. what is your take on the divot in the thing? Ignoring that it is a rock at all.. it was formed against something that made a dent in it..Therefore in my little mind it was formed in an imperfect mould , if you may, and if that is the case could it be just a rock? or was it formed in some kind of a case or hole.

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painshill

I certainly don't disagree with you but I have to ask.. what is your take on the divot in the thing? Ignoring that it is a rock at all.. it was formed against something that made a dent in it..Therefore in my little mind it was formed in an imperfect mould , if you may, and if that is the case could it be just a rock? or was it formed in some kind of a case or hole.

Unfortunately, we don't have a really sharp shot of that "dent", but is it really from the rock being moulded against something? As opposed to say a chip being taken out of it which has then been stream rolled? Or some geological feature which has been exposed inside it as a result of chipping? We still don't know if it's a rock type which could conceivably have a vestigial fossil in it.

Here's the best I can do by enlargement, sharpening and colour edge enhancement:

post-6208-0-25588500-1374771816_thumb.jpg

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Mr_ed

The edges are pretty rounded and give the impression of a footprint more than a chip. I have a Fraser River polished rock and a close up of a polished chip divot to compare..see below. I really get the impression that the mark on that rock was made by whatever it was formed against rather than a chip that was removed. A chip would have one side sharp and the other tapered .. likely. It doesn't seem to me that a chip of that design could have came out of that rock and then the divot bee sandblasted by nature to polish or smooth the inside of the divot evenly so as to make it look like a footprint or an impression.

I am sayin that with only experience in collecting .. not in study.. so I am by no means an expert, just not a beliver ... yet ..

No 1 is a Fraser River polished rock and no 2 is a close up of the divot that is in no 1

Cheers

Ed

post-10180-0-75771100-1374774213_thumb.jpg

post-10180-0-37609200-1374774239_thumb.jpg

Edited by Mr_ed

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JohnJ

Fractures and chips in various types of rock can appear to be a "dent" or impression. It just depends on how long it has been smoothed by natural forces. The larger brown rock to left of center in this photo could look like it has impressions to some, but they are just polished conchodial fractures.

post-420-0-35605000-1374779052_thumb.jpg

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Mr_ed

For a rock to chip like that it has to have certain conchodial qualities, does it not? That one in the picture appears to be layered. A layered rock would never chip and polish like the brown one in your picture.

Interesting picture.. lots of volcanic type rock and even appears to be obsidian there.

Cheers

Ed

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Auspex

I think it is safe to say that everything about this rock is well worn, and to me the appearance of the 'dent' is consistent with a well worn chip.

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painshill

And just for good measure, here's one of my Moqui concretions that has a "divot" chipped out of it that has partially weathered:

post-6208-0-63510500-1374781598_thumb.jpg

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Mr_ed

What makes you believe that that hole or divot is chipped out? Looks like something softer than the matrix has worn out to me.. I am not saying you are wrong.. but what is it about that divot that that I can hang my hat on, that it is evidence that it is chipped out?

Thanks

Ed

Edited by Mr_ed

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painshill

What makes you believe that that hole or divot is chipped out? Looks like something softer than the matrix has worn out to me.. I am not saying you are wrong.. but what is it about that divot that that I can hang my hat on, that it is evidence that it is chipped out?

Thanks

Ed

Both things are true. These concretions often form in sandstone on the top of a mineralised "stalk". In rare cases you can see them eroded out of the sandstone intact and sitting on top of their stalks like bizarre rows of flowers in bud or tall mushrooms - especially the larger ones. It's the snapping off from that stalk which typically creates the chip or bite, exposing some of the interior layering. Sometimes the chip results from two concretions that have grown together creating an hourglass shape that then breaks apart. It's the broken area that then acts as the starter for subsequent erosion and - as you say - the softer layers erode more rapidly to create interesting patterns.

Edited by painshill

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Mr_ed

You guys are working overtimne on this.. that's great, but what about a streak test and a estimate of the hardness that you have asked for..seems like that is imperative for a ID. Could the owner supply such information to cut down speculation or would that hurt the specimen?

Cheers

Ed

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JohnJ

For a rock to chip like that it has to have certain conchodial qualities, does it not? That one in the picture appears to be layered. A layered rock would never chip and polish like the brown one in your picture.

Interesting picture.. lots of volcanic type rock and even appears to be obsidian there.

Cheers

Ed

Thanks. That gravel was located in eastern central Texas - very little if any volcanic rock shown. No obsidian. Cherts, jaspers, other sedimentary rocks and quartz of varying forms...plus the partial mammoth tooth. It's interesting how we like to relate isolated rocks to those found in our local areas.

Regarding the subject rock of this topic, mickiver says it was found in eastern South Dakota. So, it is most likely from a Pleistocene glacial deposit and would have been subjected to a lot of erosive forces no matter it's true composition.

Studying the last 3 photos, I'm not seeing any of the "layering" referenced in earlier posts...not that it isn't - I just don't see it. What I think I can see in those images are subtle hints of circular conchodial fractures across the surface. In a few areas, it appears that a different lighter mineral is exposed on the surface as irregular shapes. Maybe mickiver can provide additional info. This is one of those interesting finds that allows teaching and learning for many who surf this forum.

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AgrilusHunter

Studying the last 3 photos, I'm not seeing any of the "layering" referenced in earlier posts...not that it isn't - I just don't see it. What I think I can see in those images are subtle hints of circular conchodial fractures across the surface. In a few areas, it appears that a different lighter mineral is exposed on the surface as irregular shapes.

I'm in agreement with John. I don't see any layered structures either.

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Mr_ed

I'm in agreement with John. I don't see any layered structures either.

Look at picture in post no. 5 It is either layered or has parallel lines running through.. as auspex's post # 44 suggests. The bruises in picture #2 appear to me to indicate the effects of having been hit against other rocks somehow... There is no bruising in the larger divot and there should be if it was something chipped out...if it shows faint bruising on small hits it should show more bruising on a larger hit... just my opinion.. I am not convinced that the large impression is a chip.. that doesn't mean that I profess to know anything it just means you haven't convinced me and you usually do that easily.

Cheers

Ed

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AgrilusHunter

Hi Ed,

I had a close look at that and I still don't see any clear layering. I see parallel lines in places but those look like scratches in the rock to me, not layers. Considering that whole area is full of glacial till that would make a lot of sense.

Edited by AgrilusHunter

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