Vesicles and a glassy matrix containing tiny plagioclase microlites separate this scoria's partially fragmental, partially resorbed, sometime poikilitic, sometimes glomeroporphyroclastic phenocrysts of plagioclase and pyroxenes.
The majority of this thin section is a mosaic of inequigranular, anhedral hornblende and highly-poikilitic k-feldspar. Though a few large, irregularly shaped masses of prehnite are interspersed amidst the hornblende and k-feldspar, most prehnite is concentrated along a single vein that runs the length of the thin section. Some of the prehnite shows anomalous blue extinction.
The olivine that is so conspicuous in the JPN-3 handsample is conspicuously absent in thin section and represented by a mere 1 or 2 grains. Rather, phenocrysts of plagioclase and pyroxenes dominate the phaneritic phases. Both phases are subhedral and the plagioclase in particular indicates several different generations of growth. Some plagioclase is concentrically zoned, though most grains contain alternating inclusion-rich and poor zones. Inclusions are of pyroxenes and glass blebs. The groundmass contains glass, plagioclase microlites, and tiny pyroxenes.