In the unit cell of galena six square faces of equal size each form 90 degree angles with every adjacent face. What type of crystal system is this?

The unit cell of galena, with its six square faces forming 90-degree angles with adjacent faces, belongs to the isometric (or cubic) crystal system. This system is characterized by three equal axes intersecting at right angles. Galena specifically crystallizes in the cubic lattice structure, which is typical for many minerals with a similar symmetry.