How is a record of magnetic reversals recorded in molten rock at mid-ocean ridges?

Record of magnetic reversals recorded in molten rock at mid-ocean ridges:

Often in ocean, at the junction of two plates, lava often comes out of the junction because of the movement of plates away from each other as a result, forming a divergent plate boundaries. As the lava comes up, the magnetic minerals come along with it.

During the molten state, they arrange themselves along the magnetic poles of the earth. Then they gets solidified. As the magnetic reversals take place in earth, these rock can't change the orientation, but they retain the data about the magnetic orientation of earth corresponding to the date of their formation.