Occurrence thumb|left|Monazite sand The concentration of erbium in the Earth crust is about 2.8 mg/kg and in seawater 0.9 ng/L. (Concentration of less abundant elements may vary with location by several orders of magnitudeAbundance of elements in the earth’s crust and in the sea, CRC Handbook of Chemistry and Physics, 97th edition (2016–2017), p. 14-17 making the relative abundance unreliable). Like other rare earths, this element is never found as a free element in nature but is found in monazite and bastnäsite ores. It has historically been very difficult and expensive to separate rare earths from each other in their ores but ion-exchange chromatography methodsEarly paper on the use of displacement ion-exchange chromatography to separate rare earths: developed in the late 20th century have greatly reduced the cost of production of all rare-earth metals and their chemical compounds.
Occurrence thumb|left|Monazite sand The concentration of erbium in the Earth crust is about 2.8 mg/kg and in seawater 09 ng/L. (Concentration of less abundant elements may vary with location by several orders of magnitudeAbundance of elements in the earth’s crust and in the sea, CRC Handbook of Chemistry and Physics, 97th edition (2016–2017), p. 14-17 making the relative abundance unreliable). Like other rare earths, this element is never found as a free element in nature but is found in monazite and bastnäsite ores. It has historically been very difficult and expensive to separate rare earths from each other in their ores but ion-exchange chromatography methodsEarly paper on the use of displacement ion-exchange chromatography to separate rare earths: developed in the late 20th century have greatly reduced the cost of production of all rare-earth metals and their chemical compounds.