We have carried out first principles structural relaxation calculations on the hydrous magnesium silicate Phase A (Mg 7 Si 2 O 8 (OH) 6 ) under high pressures. Our results show that phase A does not undergo any phase transition upto ~ 45 GPa. We find that nonbonded H---H distance reaches a limiting value of 1.85 Å at about 45 GPa. The H---H repulsive strain releasing mechanism in Phase A is found to be dramatically different from the hydrogen bond bending one that was proposed by Hofmeister et al 1 for Phase B. It is based on the reduction of one of the O-H bond distances with compression
