FMF - Friends of Minerals Forum, discussion and message board

[mike nunes]

Hi!
I would appreciate the help to identify this rock. I'm completely ignorant of minerals and despite research done, still can't figure it out.
I found this rock at the beach and it stood out because it was the only black rock (really black) there. Also, with a small white stone we scratched it and was like writing with great definition.
It is extremely heavy for its size, it seems to me:
Weight: 17,2Kg
Size: 35cm x 25cm x 25cm
Also, one can see extremely small glitter points (black ones it seems to me) in parts of the stone.
Any help identifying this rock is welcomed because I'm completely lost here...

[Bob Carnein]

The first step in identifying any rock is to break it and expose a fresh surface. Then, unless it's very fine grained, try to identify the minerals it's made up of (it helps a lot to have a 10X magnifier or low-power binocular microscope). It's definitely odd that it was the only one there. Something I noticed in your photos is that there may be a couple of "inclusions" in it. A guess, without much to go on, is that it may be basalt. But there are other possibilities.

[James Catmur]

Once you have a fresh surface try a few tests to see what minerals are present

https://www.mineral-forum.com/message-board/viewtopic.php?p=19487#19487

If it were from an area with vulcanism I would also say basalt. Beach finds can be from miles away and may have been brought in as ballast or beach reinforcement, from say Madeira.

[mike nunes]

Thank you for all the help, James and Bob!

I did a bit more research on it, and contacted more people from the area of expertise, and I'm inclined to basalt but am not sure. A contact told me that it could be a ballast stone, but no way to be 100% sure.

Anyway, seems difficult to have any worth except decorative and I will hang on to it and maybe use for a sculpture. It is so uniform and smooth that it would be a shame to waste it.

Maybe when I start to work it I will come across some surprise. If so, rest assured I'll be back for updates, promise.

And now I'm a fan of this forum and will be following it for all the right reasons...

Again, thanks for the help and see you around!

M

[James Catmur]

Um prazer

I spend time on the beaches of Fife, Scotland and there is a lot of similar material there often showing the classic 6 sided shapes. Some blocks are huge (2 tonnes?) and they all get a great sea worn shine