igneous-rock
Filter by:
Source
State or Territory
Back
igneous rock
HB50
crystalline or glassy rock formed from a molten rock mass (magma) which has cooled and solidified within the earth’s crust (plutonic rock) or has been ejected to the surface (volcanic rock)
The principal igneous building stones are basalt, granite and trachyte. Igneous rocks are further subdivided into: Acid rocks (containing 65 % or more of silica); Basic rocks (containing 45 to 52 % of silica); and, Intermediate rocks (containing 25 to 65 % of silica).
See also: metamorphic rock