Field of Science

A geologist riddle #3

Another geo-riddle, this time a bit challenging...

The photo shows a contact between a greenish in the foreground and a much brighter brownish lithology in the background. The appearance of these rocks reveal that they must have experienced some hard times in the past, but the contact is not the result of tectonic forces.
The green rocks contain a secret, revealed by some creeks in the landscape- a secret which brought great wealth to the inhabitants of the valley...


  1. My Alpine geology is very rusty (as it appears, are the streambed stones in the last photo). Since the streams reveal the secret, I suspect it must be in the form of placer minerals derived from the local bedrock. Gold would be an obvious choice, presuming these green and brown rocks are mafic and ultramafic, respectively, but a bit of web searching turned up a reference to emeralds emanating from chloritic schists from this region, and I'd imagine they'd make a panner wealthy, as well.

  2. It´s very close, but not yet the correct raw material (it´s more humble, even if today it has became again a very important material)

    There are emeralds, but not in this tectonic unit, and therefore not in this area ( however it´s only some kilometres) - here some thougths on the emeralds of the Alps:

  3. I'm going to venture a guess that it represents a source of copper for early tools.


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