Economic caesium deposits are extremely rare. They only occur in extremely differentiated lithium-caesium-tantalum (LCT) pegmatites.
Only two mining operations worldwide have produced commercial quantities of caesium bearing ore (pollucite). In 2018 a third deposit was mined in Western Australia.
This pegmatite consists of an outerwall zone that is coarse grained, and dominated
by plagioclase feldspar, muscovite and quartz with other accessory minerals; and an inner core zone composed of quartz, albite (cleavelandite), lepidolite, pollucite, petalite,zinnwaldite, eucryptite, beryl and amblygonite. The corezone is ‘capped’ by a thick potassium feldspar zone.