Étymologie Du latin semi-.
Préfixe semi- /sə.mi/
Indique l’idée de moitié, synonyme : demi-, hémi-, mi-. Os, cartilage semi-lunaire.
Indique une incomplétude, l’idée de « presque », synonyme : quasi-. Une steppe semidésertique.
Imperial College Rock Library
une utilisation anglo-saxonne ?
Glossary: Pelite Synonyms: metapelite
Pelite is a term applied to metamorphic rocks derived from a fine-grained (<1/16 mm) sedimentary protolith. The term usually implies argillaceous, siliciclastic sediments as opposed to carbonate mudstones. Pelite is sometimes used as a rock name for metamorphic rocks whose classification is unclear, it is also used as a prefix for a metamorphic name, for example, pelitic schist, although this usage is not recommended since it is based on an interpretation. Metapelite is sometimes used as a synonym for pelite since strictly speaking the term pelite applies to the protolith of a metamorphic rock. The corresponding term for an arenaceous protolith is psammite.
Metamorphic rocks with protoliths consisting of mixtures of sand and mud grade materials are described as semi-pelites. The term metasediment is also used for metamorphic rocks with sedimentary protoliths. The sedimentary rock name can also be prefixed with meta, such as metasandstone. Related Terms metamorphic rock, psammite
http://www.mern.gouv.qc.ca/publications/mines/publications/publications-2008-1c.pdf