What rock is this??

HerrScheisse

Hi,

Could anyone help me identify this rock? It is from a beach and is dark and smooth like glass, on first appearance black but has a slight dark green hue on the thinner pieces. There is also an outer coating, I assume some kind of calcium deposit.

My initial thought was basalt but it seems too smooth for that.

Any ideas? Thanks

DeepSleeper

Flint - the outer 'coating' is called cortex...

HerrScheisse

Many thanks for the answer! Good to know as I found it an unusual rock to find on the beach. :pac:

bawn79

Hi hope its ok to add to this thread, my dad found this rock in the back garden in North Tipperary.

We did the meteorite test on it and unfortunately doesnt seem to be. It seems to have some kind of metal in it but isnt magnetic.

Hopefully someone might be able to help.

DeepSleeper

Rather than being a rock as such, it could be some form of slag - either from glass production or from the smelting of a non-ferrous metal, eg copper.

Sometimes slag looks like the inside of a Crunchie bar, sometimes it appears to be glassy, sometimes it is magnetic and sometimes it isn't... sorry I can't be of further help...

bawn79

Thats interesting also, my parents built a house on this field in the 1980s before that it was just used for grazing for horses.
I wonder how a piece of slag came to find its way into the middle of the field? Any one have any theories, Im wondering about blacksmithing or something like that myself.
Anyway to tell what material it actually is? For example testing for copper etc?

slowburner

Was there mining nearby?
Slag sometimes ends up in the weirdest places. I've often picked up pieces myself and carried them home. After a while the OH throws them out - it'll probably give the archaeologists a headache when they decide to excavate here. There's an old disused road near me where the builders must have used spoil from a mine - it's full of slag and other wonderful things.

bawn79

Thanks for looking slowburner - wouldnt have been any mining nearby no so its kinda odd.
My dad actually worked in the Silvermines in Co. Tipp (20 miles away) for a good number of years but he is fairly sure he wouldnt have brought anything like that back (and he knows the main types of stuff they were digging and he doesnt believe that the 'slag' would have been unusual looking enough to bring home with him) and particulary he wouldnt have deposited in the middle of a field. So its kinda a strange one.

DeepSleeper

Don't be put off by the idea that it was found 'in the middle of a field' - Many archaeological sites are not found until the NRA decide to put a road 'through the middle of a field' - I heard somewhere that they find an average of one 'new' site per kilometer of new road they build, so there may have been an old settlement or small industrial site (historic or even prehistoric) in the vicinity (even in the field itself) and this may account for the discovery of the piece of (possible) slag. It can be amazing what lies under the topsoil...

slowburner

bawn79 wrote: »

Thanks for looking slowburner - wouldnt have been any mining nearby no so its kinda odd.
My dad actually worked in the Silvermines in Co. Tipp (20 miles away) for a good number of years but he is fairly sure he wouldnt have brought anything like that back (and he knows the main types of stuff they were digging and he doesnt believe that the 'slag' would have been unusual looking enough to bring home with him) and particulary he wouldnt have deposited in the middle of a field. So its kinda a strange one.

I find this link amazing for researching physical history. It will bring you straight to Silvermines in approx. 1838. It might give you a clue as to activities which might have caused slag to be deposited there in the past. Keep an eye for terms like 'level' and 'shaft' which indicate mining activities. If you haven't used it before, you can zoom in and change the map to aerial photos from 2005, 2000 and the later 25" map (1895'ish). Taking your time with it and changing the views reveals a colossal amount of information. You might be surprised.;)

bawn79

Well we have come up with a theory, a neighbour that lived to the next boundary of the site worked in a previous incarnation of the silvermines probably sometime in the 50s / 60s and we think it may have some link to him, maybe he flung it into the empty field next door. Another potential option is that it came in topsoil to the site.

I had looked at the OS maps website before but never for the Silvermines area, I found it really interesting (and particulary my dad loved it) so thanks for that.

donzenettii

DeepSleeper wrote: »

Flint - the outer 'coating' is called cortex...

I have seen pieces of this rock many times while walking on the beach and would never have thought of it as flint,...thanks for the answer DeepSleeper