FMF - Friends of Minerals Forum, discussion and message board

[Pete Modreski]

I'd like to try to get the advice of some of my knowledgeable international friends here, to comment on just what these pebbles are, that the sister of a friend of mine, brought back from a trip to Elba. I was told that "she had brought back some interesting pebbles" from Elba, that they were sure I would like to look at, and perhaps I could tell them more about what they are. They had been told that "these pebbles were unique to Elba", and were unusual, but beyond that, they did not know anything specific about what they were supposed to be.

I am attaching a picture of the pebbles, plus a close-up of the largest pebble. As you'll see, they are of a solid white, apparently very fine-grained, porcelain-like material, with some small (1 to a few mm across), pale blue "snowflake-like" spots, and some with some larger, similar, but black spots. I don't think I've ever seen any rocks or pebbles quite like this. The pale blue patches "could" be crystalline patches or aggregates or blue elbaite, and the black patches could be crystal clusters/rosettes of black schorl tourmaline. (In one of the pebbles illustrated, the black patches look more like brecciated fragments of some black rock; in others, more like radiating crystal-growth aggregates.) The white matrix rock of the pebbles "could" be a type of aplite. You'll see that the largest pebble also contains smaller, pale brown grains of some other mineral, not readily recognizable to me as to what it might be.

Has anyone seen rocks or pebbles like this, from Elba? I told my friend, of course, that Elba is famous for its gem pegmatites, and that the colored tourmaline species elbaite is named for it, but, other than as background knowledge, this did not help them much as to understanding just what the pebbles are. I actually even wondered, if these are necessarily natural (vs. something artificial) pebbles. I do not have any idea, where on the island they obtained these pebbles. I "presume" (but do not know for certain) that they found these on a beach or river, as opposed to just having been given to them by someone (or purchased??).

I'd appreciate any comments some of you might have, who are familiar with pebbles like this. Thank you!

[alfredo]

Pete, does the white porcellanous matrix fluoresce dull red under SW UV light? (If so, it's probably feldspar and an aplitic or pegmatitic origin is more likely.)

[marco campos-venuti]

The pebbles are from Capo Bianco beach, north of the Island, near Portoferraio and are constituted by the Capo bianco aplite dike dated 8.4 My, before the main granodiorite pluton of Monte Capanne dated 6 My, where the elbaite bearing pegmatites are found. The blue spots are aggregates of indicolite tourmaline.
There is a rich literature on this rock, you can google it.

[marco campos-venuti]

I realized there is an intruder in your pile of rocks. It is a brecciated marl from the Elba Flysch (Cretaceous). The white stripes are of calcite.

[Pete Modreski]

A wonderful reply, Marco, thank you very much! I had guessed that someone on the forum would be familiar with these and know just what they were. Yes, that one pebble with the white veins cutting the dark rock fragments, is rather much different!