Abstract
Most of the Antarctic micrometeorites (80%) contain hydrous silicate (Engrand and Murette, 1998). However, hydrated meteorites are only about 3% of that falls onto the earth. On the other hand, 30-40% of asteroids contain the hydrated mineral. In order to explain the difference of such relative existence level of hydrated minerals, we performed impact experiments onto hydrous and porous targets and to examine effects of dehydration of hydrated minerals in the dust formation by high velocity impact.