Abstract
Structure and nature of air-hydrate crystals found in deep ice cores from Dye 3, Greenland are summarized. Those crystals were formed by a reaction between ice and air under high overburden pressure in the ice sheet. The crystallographic structure is the Stackelberg's structure II, which is one of the two distinct structures of clathrate hydrates. In the structure, individual gas molecules are encaged in polyhedral cages formed by water molecules. Growth process of the air-hydrate crystals in the ice sheet is well understood by a theoretical consideration of nature and behavior of air molecules in ice and in clathrate hydrate. The consideration is made on the basis of the data on the distribution and shape of the natural crystals in the ice sheet as well as artificial crystals grown in a high pressure vessel. Some numerical calculations are also made for estimating a growth period of the crystals.
