Gaseous Species in Equilibrium with the Apollo II Holocrystalline Rocks during their Crystallization

Abstract

THE holocrystalline rocks from the Apollo 11 landing site in Mare Tranquillitatis characteristically contain vesicles and vugs¹ which must have been maintained by an internal gas pressure balancing the overburden pressure. Although the landing site may contain rare fragments from distant craters¹, the common rock types of the Apollo 11 sample are probably of local origin. There are no craters closer than about 50 km which could have excavated samples from more than a few hundred metres depth. The groundmass grain size of the holocrystalline rocks, which is from 0.1 to 1.0 mm, and up to 3 mm in vuggy areas¹, also suggests extrusive or hypabyssal crystallization for these rocks. Crystallization probably took place at depths greater than a few centimetres and no more than two kilometres. The total pressure, which was equal to the gas pressure in the vesicles and vugs of the Apollo 11 rocks, was therefore between 0.01 and 100 atmospheres.