scoria - large hand/display specimen of basalt scoria from the 2018 lava flow that buried Kapoho, Hawaii
Scoria is the silica poor equivalent of pumice. Lava with a low silica content is runny, so gas bubbles tend to coalesce to form larger bubbles in basalt. In a silica rich granitic magma, high viscosity prevents bubbles from coalescing, so there are many more, but smaller, gas bubbles in pumice, one reason it floats longer in water.
Near the top of a flow, gas bubbles form because of the reduction in pressure. These become frozen in place to form scoria.
Deeper in the flow the basalt is more dense, with smaller bubbles, or even none. As an aa flow progresses, chunks of scoria and blocky lava tumble down the advancing front and are either bulldozed ahead by the advancing flow or are covered.
This scoria was collected from an aa field at the edge of the 2018 Kilauea flow channel that almost engulfed the Puna geothermal plant, that buried the community of Kapoho and that eventually filled in Kapoho Bay completely.
Impressive specimens, both for their size, light weight, and for the size of the vesicles. The pencil is 5 1/2" long, for scale.
Select a specimen: When there is more than one specimen shown, you can select a particular specimen by telling us what is in the photo with it, a blue or black and silver pen, a black mechanical pencil or one of those plus some number of coins, or you can let us make the selection.
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