n combining form
(Geological Science) (in mineralogy) indicating a particular type of cleavage: plagioclase.
[via French from Greek klasis a breaking, from klan to break]
a combining form used in the names of minerals with a particular cleavage, as specified by the initial element: oligoclase; plagioclase.
[< French < Greek klásis breaking, fracture = kla-, s. of klân to break + -sis -sis]