Plates on either side of the Mid-Atlantic Ridge are oceanic plates.

Mid-ocean ridge or mid-oceanic ridge

Its oceanic crust

Granitic crust does not form at the mid-oceanic ridge. Rather another type of igneous rock Basalt is formed at the Mid-Oceanic ridge. Both are silicate rocks and have a high oxygen and silica content. The difference is that Granite is formed intrusively, that is within the Earth's crust. Basalt is extrusive, that is it is formed above the Earth's surface, such as at the bottom of the ocean at the Mid-Oceanic ridge.

The Oceanic Crust close to the Mid Ocean Ridge is thinner than that Oceanic Crust far away from the ridge. This is due to tensional forces, as a result of crustal expansion and rock fracturing during the formation of the ridge.
the oceanic crust is thinner