porous

definition: 
(Of a rock or other material) having minute interstices through which liquid or air may pass
sentence: 
The result is the formation of solid structures of a porous calcium carbonate rock also known as travertine. Mudstones are the main source of oil and gas, although by the time the oil or gas is extracted it has usually migrated to porous rocks such as sandstones of limestones.
difficulty: 
easy
toefl frequency: 
2
toefl classification: