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. 
Mahogany Obsidian is grounding but also energizing.  It can aid in bringing forth the energy of growth and creativity.  Helps with forgiveness of self, confidence, setting boundaries, and finding workable solutions.  Used in past life and ancestor work, inner journey, and retrieval work.
Chakras:  Root, Solar Plexus, and Crown