This is a quartz, more exactly a transluscent chalcedony (itself a variety of cryptocrystalline quartz) which shows concentric bands sometimes containing opale. Comes in many colors, banded, forming concentric bands, more or less circular up to oval.
Their formation is so far discuted : or by gradual filling and rhythmic crystallization in the cavity of rock or the formation of the agate and of the rock are simultaneous or colloid solutions, rather than liquids, would flow through the agate walls.
Its name is supposedly derived from the river Achates, in Sicily, where it was discovered, but also from the arabic word for “new born tangled hair”.
The Egyptians made necklaces, sacred scarabes with agate. This was one of the twelve stones of the High Priest, Aaron’s quadrangular pectoral, symbolizing Asher, Zilpa’s son. The Greeks made wonderful cameos, imitated by the Romans who cut bowls and vases out of agate, such as the ewer conserved in the Louvre.
At the Renaissance, bowls, vases, and other kind of objects were the pride of the princely courts, especially at Florence where we can still see beautiful mosaics. its workmanship, in the Palatinat, goes back to the 1500, thanks to the deposits (now worked out) and to the presence of water to animate the sandstone grindstones for the polishing.