OLIVINE CRYSTAL SEGREGATIONS IN LUNAR GLASS WITH THE COMPOSITION OF PYROXENE

Abstract

Natural glasses are most informative for interpreting processes of ordering and crystallization of magma. Glassy rocks are formed under conditions that are far from being in equilibrium, because vitrification occurs upon fast cooling, before which the melt is mobile, and vitrification of the melt may 'freeze' different stages of its evolution and crystallization. The authors studied a green lunar glass fragment, 0.2 mm in size, transparent, lacking visible inclusions and having conchoidal fracture. One of its surfaces resembles the wall of a gas bubble. In transmitted light under the microscope, the glass is isotropic and homogeneous. Such glass usually is defined as volcanic. The analysis was done under a JEM-100C transmission electron microscope, equipped with a goniometer with a ±60° dip angle and the Kevex-5100 energy-dispersion attachment. Study results are discussed, and the data suggest that crystals possibly grow by a two-stage mechanism if the magmatic conditions are not in equilibrium. In the first stage, elementary amorphous segrations will form and conglomerate in the melt, and, in the second they will become structurally organized. Each stage, in turn, could also have several phases.