The Rock - Scoria
- Igneous Rock Type:
Extrusive
- Related to: Basalt,
obsidian,
pumice
- Chemistry: Basic to intermediate
- Color: Black, brown to red
- Texture: Glassy
- Origins: Volcanic lava flows and ejecta
- Common Minerals: N/A
- Accessory Minerals: N/A
- Uses: Decorative stones, grilling stones
Scoria is
a textural rock type and not a rock that is classified by mineralogy or
chemistry. It forms from lava that is rich in volatiles or gases but
is less viscous than a pumice forming
lava. When the molten rock is rising in the volcanic pipe, gases begin
to form and collect and those gases form large bubbles in the lava. The
resulting solidified rock is scoria. Although the open spaces in scoria
can be large the rock is generally heavier than water, unlike most pumice which can float on water.
Some scoria forms from lavas that flow out of a volcano and some scoria
can be pyroclastic. Pyroclastic rocks form from lava that is ejected
from the volcano. Scoria (which is also known as cinder) is the primary
component of cinder cones. A cinder cone is a small but very
common volcano type. Cinder cones have also been called scoria
cones. Cinder cones rarely grow very large, but form sometimes
very symmetrical cone-shaped hills.
Scoria does not have a lot of uses. In fact the name is derived
from a term for waste. However it can be used as an interesting decorative
stone with some reddish color. Some of the large Easter Island statues
called Moai have scoria stone in their designs.
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