Cinder/Scoria
Cinder/Scoria is a collective name of cinder/scoria -shaped
fragments produced by a volcano. Most of the
cinder/scoria is highly vesicular, generally black,
dark brown or purplish red, and in composition of basaltic or andesitic.
It can't float on water because its density is larger than that of water and acidic pumice. There
are two mechanisms of formation of Cinder/Scoria.
In one mode (Cinder or Scoria), when the
liquid lava fragments full of gases were erupted
and solidified in the air, the dissolved gases out of
lava fragments expanded and escaped, while leaving
holes or vesicles in lava and forming cinder-shaped
appearance. This kind of cinder-shaped fragments often fell around
volcanic craters. In another mode (Scoria), the
solidified vesicular outer shell of lava flows or volcanic bombs cracked
and produced scoria. Here the scoria-shaped fragments were
formed by the second mechanism. Besides, scoria is a kind of good natural
heat-insulating material.