Associated with gabbroic intrusions. Greenstone - aphanitic weakly metamorphosed mafic igneous rock with a basaltic protolith. Dominated by epidote, chlorite, actinolite and carbonates. Na amphibole and rock becomes an amphibolite. Greenstones are the product of sub-seafloor alteration of basalt.
Alteration is often patchy and fracture-controlled.
The term spillite is often used interchangeably. Serpentinite - metamorphosed ultramafic rocks. Probably forms in much the same manner as greenstone and the two are often intimately interlayered in older Archean terrain. Classic area is the Franciscan Complex of California and Santa Catalina Island. Protolith for blueschist is predominantly graywacke, lesser chert and basalt.