the scoria has been expelled completely from the mercury
Some of these cones are now barely recognisable, having been excavated for the volcanic cinder, scoria , used to build the roads of Auckland.
It's always slightly warmer on Rangitoto thanks to the black scoria , but the 360 degree view of the gulf and the volcano-studded cityscape of Auckland is matchless.
Small vesicular pieces of volcanic material, scoria , collect around the vent to form a cinder cone.
chunks of black scoria
Alluvial, colluvial or chemically formed gravel, clayey gravel, sandstone, limestone, tuff, scoria are examples of marginal materials.
Amygdaloidal cavities are located immediately below the uppermost scoriaceous part of the second flow, near its contact with the overlying flow.
On the western side of the mesa, black hornblende xenocrysts several centimeters in size are also found in a scoriaceous , agglomeratic portion of the lava flow.
The fine-grained ash groundmass contains equal proportions of scoriaceous tachylite and palagonite with basaltic lithic fragments.
They can be traced for more than 40 miles, and for most of the strike length it is a thin, sandy or ‘ scoriaceous ’ bed, ranging from a few inches to a few feet in thickness.