Trachyite is the extrusive equivalent of syenite.

They are all extrusive igneous (i.e. volcanic) rocks of intermediate to felsic composition.

Gabbro.

The vast majority are carved from compressed volcanic ash called tuff, but basalt, red scoria and trachyte or feldspar were also used.

The majority were carved from tuff (a compressed volcanic ash) from the Rano Raraku volcano (there are also 13 moai carved from basalt, 22 from trachyte and 17 from fragile red scoria)