Callaïs is the name of a green stone used for making beads by western European cultures of the later Neolithic and Early Bronze Age. It was described by Pliny the Elder (NH XXXVII.lvi.151) as being paler than lapis lazuli.
Its source was probably Brittany, near Locmariaquer where numerous turquoise items have been found, although this has not been confirmed.
References
Callaïs Wikipedia(Text) CC BY-SA