It is a beautiful menilite opal kidney from Ménilmontant in Paris (France). Ménilmontant is a neighborhood in eastern Paris.
This stone is called menilite because it was described at Ménilmontant (first reported in 1787 by Delabre and Quinquet), where it exists as concretions in the bituminous residues of the Oligocene. In Ménilmontant, the menilite kidneys are found in a papyraceous clay in the dry state, sticky in the wet state. Once released from their gangue, they present on their edge traces of the schistosity of this one.
Specimens from the Aristide Gouverneur collection (XIXth century).
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