The grain size is finer in the pillows than in the massive flow layers. Chilled margins with devitrified glass rims on pillows and flows are well exposed. Primary minerals are plagioclase, clinopyroxene, olivine and very fine-grained magnetite. Accessory minerals include apatite and subordinated Cr-spinel and zircon. Secondary phases are in general celadonite, saponite, smectite, zeolites, calcite, and Fe-oxyhydroxide.
Alteration is slight with filling of vesicles and scarce replacement of groundmass.