Malas are traditionally used to aid in meditation.  These have the traditional 108 beads on them and the belief is to repeat your mantra/prayer/chant as you touch each bead to reach a deep sense of peace and calm. 
White Agate can aid in harmonizing feminine and masculine energies within.  It can help improve concentration and logic and allow for work to release traumas and courage to trust self and others.
Chakras:  Crown