FMF - Friends of Minerals Forum, discussion and message board

[Sarah.S]

This stone was found washed up on a beach in Central Portugal recently. Can you please help me to identify it? The top stone is finer than the stone which looks like granite underneath. It all looks to be completely merged as if it is one stone. Could it be a natural formation of design and colours? The photo is limiting but your ideas would be greatly appreciated. Thank you."

[keldjarn]

Hello Sarah,

It can be difficult to identify tumbled stony objects found on beaches. I suspect you have found a man-made object of some kind. The patterns and composition seems to be too symetrical to be natural.

[Sarah.S]

Thank you keldjarn for your feedback. I agree the patterning suggests that it is man as, but there is no sign of separate pieces being used as it all looks like one piece. Can this happen over time? It also looses its symmetrical pattern around the edge. Im unable to identify how the top patterned mineral is attached to the lower stone. Any further ideas would be helpful.

[keldjarn]

Sarah,
it is only guesswork, but it looks like a piece composed of two layers. One could be a natural rock ( i.e. a granite as you propose). On top of the rock 3 coloured (cement-based?) materials have been applied in a pattern. It could be from a decoration of a stony floor or wall (?).

Knut

[Sarah.S]

Hi knut,
Thats really helpful. In that case it may be that I can rule out the possibility of it somehow being a natural mineral formation. However the method that could have been used to make it is still beyond me! Thanks for your time and consideration.

[vic rzonca]

Sarah, my guess is that your piece is part of a decorated, plastered, possibly interior, stone wall. The location indicates it could be ancient.

[Riccardo Modanesi]

Hi to everybody!
I agree with Knut: I think of an archaeological (or better: archaeomineralogical) residual. Sarah, it would be interesting if you take it to an archaeological expert (for example in a museum) in order to have it dated by radiometric methods and achieve an information about the historical period of the specimen. If natural, I think of an arenaria of the same kind of such stones you may see and admire at Petra, Jordan (very famous!).
Greetings from Italy by Riccardo.

[John S. White]

I vote for archeological relict, perhaps part of a decorative wall. Taking it to a museum is an excellent idea.

[Sarah.S]

Thank you John, Riccardo and knut for your feedback. Ive now sent an email enquiry to the Museum of London Archaeology asking if they will consider viewing and dating the stone. Im glad for this suggestion and will let you know the outcome.

Sarah

[Josele]

Dear Sarah,
Your stone is a piece of tile so-called "hydraulic" tile. Is made of two layers: a layer of fine-grained concrete and another layer of mortar colored in various ways. It was widely used in Modernist architecture and is still so common in Spain and Portugal.
Nice find anyway!

https://www.demosaica.co.uk/

[Riccardo Modanesi]

Hi to everybody!!!
Wonderful!
Something similar happened to me when I was still a boy. I found a brillant-red massive piece in a wood and took it to some mineral experts I met in my home. It was surrounded by concrete material and they told me it were a "chrome mineral surrounded by arenaria". I didn't throw it away, but I stored it in a closet. When I was at the University (some 7 years had got out) I resumed the specimen trying to achieve a hardness value and a specific weight of a small piece of the red part. The red part SWIMMED ON WATER and its hardness didn't reach the value of 2 according to the Mohs grading scale!!!
Would you like to know what was it? It was nothing else than PLASTIC MATERIAL!!! And what about the "arenaria"? Simply it was CONCRETE!!!
Greetings from Italy by Riccardo.

[Sarah.S]

Josele you have solved the mystery! ha ha I wish it could have been an ancient relic but Im glad you have saved me further time and investigation. My boyfriend and I found your link interesting.

Riccardo thanks for sharing your story, its lovely. I wonder, what is of more value.....solving the puzzle of an object, or the possibilities a mysterious object can awaken in the imagination!
Thank you all for your very helpful and encouraging contribution.

Best wishes

Sarah