Basaltic scoria is the typical product of strombolian activity. Cindery in appearance, scoria fragments have a light, frothy texture. Individual clasts are sharp-edged and angular. Normally, basaltic scoria is a greyish-black colour, but when fresh it may be stunningly iridescent, shining in peacock blue colours. Because the lava is easily fragmented by escaping gas, only a small proportion of the finest grained material is produced, so a typical scoria deposit is not dusty. Most fragments here near the Bandera cone in New Mexico are 1-3 cm in diameter. About 0.01 cubic kilometers of magma was erupted, and the eruption column probably did not reach more than a few hundred meters above the vent. Thus the deposit thins rapidly away from the vent. Because basaltic scoria is used extensively for road making, scoria cones are often quarried, displaying their internal structures, as here at Bandera. Within the cone itself, there is often well-developed layering, resulting from separate explosive pulses, but here, a little way downwind, the deposit forms a very even blanket. Note how the loose material piles up at the bottom of the quarry face, forming slopes with the same angle of rest as those of the main cone. (Section 9.4).

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