Europium anomaly

The Europium anomaly is the phenomenon whereby the Europium (Eu) concentration in a mineral is either enriched or depleted relative to some standard, commonly a chondrite or mid-ocean ridge basalt (MORB). In geochemistry a Europium anomaly is said to be "positive" if the Eu concentration in the mineral is enriched relative to the other rare earth elements (REEs) and is said to be "negative" if Eu is depleted relative to the other REEs.