It is unusual geologically because the chemistry of its lavas is virtually identical to lavas that erupt at mid-ocean ridges (a magma type called MORB, or mid-ocean-ridge-basalt) and quite different from most oceanic island lavas.
(It; is geologically; because the chemistry of its lavas is virtually identical to lavas that erupt at mid-ocean ridges) (a magma type; called; MORB)
It a magma type
is geologically called
because the chemistry of its lavas is virtually identical to lavas that erupt at mid-ocean ridges
MORB