The seventh chakra of our body is sahasrara. It is the highest spiritual center of our body, although some say if we explore the area above and beyond our head there we will find additional seven chakras.

That is to say, at the present level of evolution of humanity, we can expect an average individual to work on the basic seven chakras. In some distant future, we will hopefully be allowed to work on the next seven chakras, which are at present non-comprehensible to us.
So, the seventh energy is probably the only of the seven chakras that has not been affected in negative sense by negative influences. Therefore we can alway expect help from the higher spiritual realms of existence, which comes through this crown center at the top of our heads.
All the other centers are subject to negative as well as positive influences and energies and we have to work and grow in our spiritual development, in order to become strong enough to reject the negativities.
Even the seventh chakra sahasrara is beyond the reach of the average spiritual seeker. Once awaken this center can connect us strongly to the spiritual levels. Have you ever seen the halo portrayed around the head of saints?
This halo is nothing else but the seventh top chakra, which has evolved. It has evolved from a center dedicated to receiving Divine energies, to a center capable of irradiating Divine energies. This is due to the fact that this energy center can grow and expand if a person is devoted to spirituality without limitations.
In the oriental literature this energy center is depicted as thousand petal lotus flower which is nothing else but a Divine lotus. Having in mind that the first base lotus chakra has only four petals, you can imagine the importance and the potential of this chakra.
Crystals that are especially suited for the seventh chakra are transparent, colorless ones, with high purity and clarity. For example, you can choose rock crystal, herkimer diamond, topaz, or angelite.