What is this rock?

[sjb]

I am stumped with this rock. I have never had a rock cause such an overload on my metal detector. I have a new Minelabe Safari and took it to the beach. It signaled gold and of course we dug, dug dug. About two feet down, there were rocks, and we took them out of the hole one by one. This rock was the cause of the beeping- and every time we test it, it causes the machine to "overload" with such a strong signal. The dark grey color of the rock rubs off on our hands, and we can write with it (like it is graphite or something). There is a vein of quarts and shiny material that runs through the rock. Any thoughts?

http://s994.photobucket.com/albums/af66/sjbgarden/Rock/

Thanks!

 

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[timekiller]

Timekiller--do you have rocks in your head? Basalt is volcanic, absolutely, and that is written in stone. Just to keep the record straight and rock solid.


If it looks like schist, smells like schist, and feels like schist, it probably isn't schist if it writes on a paper plate. That is very perplexing.

Don't take it to the Geology department at the univeristy. They don't know sch.....uh,.....nothing. Too many books.

Ha!Ha! It's been a rocky day. I was thinking about gneiss & schist when writing about basalt Sorry about that.Thanks for clearing it up. Nope not born in Rocky mount.
Taker Care,
Pete,

 

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[Tuberale]

If it writes on paper, it must have a hardness of about 2-3. No. 2 pencil: hardness 2. (Gee, wonder where that came from?) But some pencils have harder "lead" which is actually graphite, and is hardness 3. So we have here a heavier than normal rock with a hardness of 2-3 and possibly golden coloration at spots.

Golden colored. Might be mica, but mica shouldn't react as metal for a detector. Try taking the point of a compass or knife, and scraping out one of the golden-colored pieces. Show us the result.

This is getting harder than it should be, folks.

 

[High Plains Digger]

I am not sure that pencil hardness is charted by the Mohr's hardness chart. I think they have a relative chart of their own. That's a lot of charting. I am glad I have graduated to a No. 3, but oh, for the days of the dark streak of a large size 1st grade no. 2 pencil. Now that was freedom. Before I hit rock bottom.

 

[sjb]

Thanks for all the humorous banter and thoughts. I think the best way to settle this will be to cut it open. We will do that when I get home (still on vacation) and post what I find. Any suggestions as to how to do that?

I have been metal detecting for years, and mostly we get coins (one from 1694 is my fav) and so this is new to me. I love to learn -and appreciate all the help.

We will let you know!

Thanks again-

SJB

 

[mile-ender]

Just wanna throw in my two cents here. I'm gonna go with magnetite. I'm pretty sure it's the same stuff that sets my detector off up here sometimes (actually quite a bit in some places :P). I read your other post though and I think your son's got the right idea - head over to the museum

 

[Tuberale]

Just wanna throw in my two cents here. I'm gonna go with magnetite. I'm pretty sure it's the same stuff that sets my detector off up here sometimes (actually quite a bit in some places :P). I read your other post though and I think your son's got the right idea - head over to the museum

Might want to read all the replies: not magnetic either. Leaves out magnetite.

 

[High Plains Digger]

If it is that soft, a hacksaw will do it, or perhaps a pocket knife. Definately not magnetite or lodestone--neither one would write on a paper plate, I don't think. I received a piece of lodestone from a guy, and he had to use a diamond blade to cut it open. I have magnetite crystals, and they are hard.

I would say we have hit rock bottom here, but that has been used. I feel like I am slamming my head against a rock wall on this one.

 

[timekiller]

If it is that soft, a hacksaw will do it, or perhaps a pocket knife. Definately not magnetite or lodestone--neither one would write on a paper plate, I don't think. I received a piece of lodestone from a guy, and he had to use a diamond blade to cut it open. I have magnetite crystals, and they are hard.

I would say we have hit rock bottom here, but that has been used. I feel like I am slamming my head against a rock wall on this one.

Yea I think calling it a rock can be ruled out.More like some kind of ore is a better name.Might even be lead zinc ore. As it can be found around that area it looks like from this map just click on it to make bigger.
http://en.wikipedia.org/wiki/File:MV-Type_and_clastic_sediment-hosted_lead-zinc_deposits.svg

 

[High Plains Digger]

Sediment-hosted lead-zinc deposits? Again, I am not familiar with out East there, but Leadville is definately hard rock (that is not a funny) mining, so I can't add much to that. But I love this thread. There I go again, getting all sedimental.

 

[Tuberale]

Will we need to peel your sedimentary layers like an onion, High Plains Digger?

Seriously, a stone that will write like a pencil almost has to be graphite, soft limestone, or dark chalk. Cutting it with a knife might be possible, if it really is that soft. Personally, though, I'd just whack it with a rock pick and sort out the largest gold-looking nuggets for further examination.

If a gold-looking nugget can be flattened with a hammer, it is very likely gold or copper (or even more likely, a combination of both).

The very dark coloration of the rock rules out most of the chalk and limestone I'm familiar with. There is very soft limestone near John Day, but it is composed mostly of diatomaceous earth and is nearly pure white. I know that when soft limestone comes in contact with metalliferous vugs there can be a lot of cooking goin' on. But I have yet to see still soft limestone with anything resembling lead (galena) or gold.

 

[High Plains Digger]

That cooking is called "Marble". Usually. Did you know that the Tomb of the Unknown Soldier came from Colorado? The quarry is literally on TOP of the Rockies--a left over of the sea that was there between the second and third (current) set of Rockies. And a new replacement piece of marble has been mined and is waiting for authorization to go.

Many times, the white stuff with galena and sphalerite and pyrite (and silver with a bit of gold in some locations) is calcite and dolomite. Leadville for sure, and I think the lead belt of MO has a lot of calcite.

 

[High Plains Digger]

You know, having a second post with this black rock, and all the other black rocks that have gone into captivity in the last day or two, it is getting rough to keep up with and keep straight. On the rocks. ANd then we have had the holey rocks. I have a headache. Can't we all just get along? Isn't there a black rock clearing house? Now I am having a bad day at Black Rock.

 

[sjb]

I emailed photos to the Harvard Mineralogical Museum and here is the response:

"Definitely a grey cobble! I'll have to see it in person to more specifically identify it. A cobble is a sedimentary particle much coarser than sand and small than a boulder."

meeting him tomorrow- will let you all know what the heck this it.

Thanks again-

SJB

 

[kuger]

Timekiller--do you have rocks in your head? Basalt is volcanic, absolutely, and that is written in stone. Just to keep the record straight and rock solid.


If it looks like schist, smells like schist, and feels like schist, it probably isn't schist if it writes on a paper plate. That is very perplexing.

Don't take it to the Geology department at the univeristy. They don't know sch.....uh,.....nothing. Too many books.

yes

 

[High Plains Digger]

This definitely qualifies as cobble by that definition. Next question is: what size is a boulder? See below. Where does gravel fit into the scheme of life? Let's cobble some answers together and get to the bottom of this matter.


A boulder is the size of a:
1. grapefruit
\2. Cantaloupe
3. watermelon
4. small child
5. Volkswagen
6. house
7. All of the above.

No need to be very specific. Just go to the gravel pit and order a load of boulders and see what you get.

Looking forward to what the museum says. What a great post. You going rock hunting again soon? I always take my detector when I go rocking, but that is mostly to give me a 3 ft. advantage over snakes.

 

[Tuberale]

Just thought of another possibility: oil shale. Could be soft and still write on paper. Hope you can file a claim on it!

 

[sjb]

Re: What is this rock? AND THE ANSWER IS.....

and the answer is....

GRAPHITE SCHIST

Moderately intense metamorphism of coal results in the conversion of all carbon chemicals in the coal to graphite (C), resulting in graphite schist. Like all schists, graphite schist has a foliated texture. The rock feels slick & greasy, has a metallic luster, is silvery-gray in color, is very soft (H = 1 on the Mohs Hardness Scale), and easily marks paper (hence the use of graphite in pencils).

The Harvard mineral man believes it to be a graphite schist- as many of you suspected. He thinks it was brought to Block Island via a glacier from RI where there are a couple of graphite mines.

I will be distributing pencils forthwith but first I may just crack open this baby to look inside.

Thanks again for all your help, this has been fun!!!

SJB

 

[High Plains Digger]

Schist. I mean SCHIST. Without looking it up, isn't schist metamorphed mica? Never heard of graphite schist, but not that important. I have seen garnetic schist in Colorado (green schist) and outside of West Yellowstone (grey), and have dug the garnets from it. I think that the chineese tourmaline I have also grew in schist (white). It looks "schisty' anyway. But the most interesting piece of schist I have has garnets in it, but they have almost completely melted. Look like pats of butter in a frying pan. I am pretty sure that the garnets occur in the mica before it becomes schist, but it may be possible that the form in the schisting process, also. The garnets in Wyo. go from nice crystaline form to 'puddles".

I'll take one of your pencils, large, red, and number two. I am feeling very regressive today. Mine never had teeth marks in it, did yours?

 

[sjb]

Schist. I mean SCHIST. Without looking it up, isn't schist metamorphed mica? Never heard of graphite schist, but not that important. I have seen garnetic schist in Colorado (green schist) and outside of West Yellowstone (grey), and have dug the garnets from it. I think that the chineese tourmaline I have also grew in schist (white). It looks "schisty' anyway. But the most interesting piece of schist I have has garnets in it, but they have almost completely melted. Look like pats of butter in a frying pan. I am pretty sure that the garnets occur in the mica before it becomes schist, but it may be possible that the form in the schisting process, also. The garnets in Wyo. go from nice crystaline form to 'puddles".

I'll take one of your pencils, large, red, and number two. I am feeling very regressive today. Mine never had teeth marks in it, did yours?

The man I spoke with is the Associate Curator of the Mineralogical Museum at the Geological Museum. I asked him if Graphite would react to the metal detector and the told me he was not familiar with how they work. When I look on line, it seems that a metal detector does not react to graphite. What do you think??

He also thought that thin line of other material is most likely mica.

"Schist", I thought we had this finished.

By the way, I just tried to open it and it is harder than I thought, with pieces coming off- and although they are wonderful writing tools, my hands are completely covered.

I will keep trying.

SJB

 

[mighty_mace]

Hmm maybe not the same 'ole schist. I was wondering why it reacted to the metal detector, as mine only finds the wonderful metal eraser ends.