Not a diagnostic property. The color of a mineral in powdered form. Streak of a mineral does not vary like color. Diamond is the hardest mineral, which means no other mineral can scratch diamond. But diamond will be shattered if you hit it with a hammer.
Cleavage is a characteristic of the bond strength of mineral.
The minerals which do not have definite cleavage planes break along fractures. Depends on the composition of the mineral. It is best to use several characteristic properties like hardness, luster, shape, cleavage, etc. for mineral identification.