Answer:

shale

Answer	Crossword Clue
SHALE	Claylike rock
SHALE	Fissile rock
SHALE	Oil source

SHALE	Oil-yielding rock
SHALE	Fine-grained rock
SHALE	Sedimentary rock
SHALE	Fuel-yielding rock
SHALE	Layered rock
SHALE	Common fossil rock
SHALE	Rock made in layers
SHALE	Oil-rich mineral

SHALE	Stratified rock
SHALE	Petroleum source
SHALE	Kerosene source
SHALE	Rock often containing quartz
SHALE	Synfuel source
SHALE	Thin-layered rock
SHALE	Source of oil
SHALE	Layered fissile rock

SHALE	Oil-bearing rock
SHALE	Rock that may yield oil
SHALE	Fracking target
SHALE	Mudstone
SHALE	Grained rock
SHALE	Flagstone material
SHALE	Source of aluminum
SHALE	Flaky rock

SHALE	Laminated rock
SHALE	Not exactly hard rock?
SHALE	River-delta material
SHALE	Fossil holder
SHALE	Rock made into flagstones
SHALE	Source of kerosene
SHALE	Fissile rock.
SHALE	Laminated rock.

SHALE	Rock.
SHALE	Fine-grained rock.
SHALE	Petrologist's concern.
SHALE	Type of rock.
SHALE	Petroleum source.