Overall, ash grains were separated with the micro stereoscope and classified into: visibly altered lithic fragments, visibly altered free crystals, dark tachylitic scoria, translucent sideromelane, and unaltered free crystals.
3) show a generalized non-juvenile composition represented by highly altered fragments of pumice, sideromelane, tachylite, and free crystals.
Figure 3D shows a stark contrast to the smooth, highly reflective inner surfaces of the sideromelane grain from the March 12, 2015 eruption shown in figure 4D that will be described later.
Figure 3F shows colorless triclinic twinned (plagioclase) crystals adhered to altered vesiculated sideromelane. Notice the orange specs of oxidation of the glass on the outer surface.
The ash from the March 12, 2015 eruption differs from the 2014 eruptions in that it shows a ~10 vol.% content of unaltered tachylitic scoria, ~7 vol.% of unaltered vesiculated sideromelane grains, as well as unaltered olivine (3 vol.%) and plagioclase (4 vol.%) free crystals.
The characteristics of the non-juvenile fragments are similar to the grains described for the 2014 eruptions, with presence of altered scoria, altered sideromelane, altered plagioclase crystals, and gypsum.
For the 2014 eruptions, EDX analysis was performed on pumice grains, porphyritic lithics, tachylithic scoria, and vesiculated sideromelane grains.
However, the grains of tachylithic scoria and vesiculated sideromelane that were considered as the juvenile fraction of the ash for this eruption (squares in figure 7), show a narrow distribution in composition ranging from andesite to dacite with silica contents between approximately 58 and 62 wt.%.
Non-juvenile components identified in the 2.7 [phi] fraction of the ashes are: altered sideromelane, altered tachylitic scoria, hydrothermally altered lithics, altered plagioclase crystals, sulphur and gypsum crystals.
The juvenile fragments in the form of unaltered tachylitic scoria, vitreous sideromelane, and olivine and plagioclase free crystals indicate that the eruptions were of phreatomagmatic origin.