inflexible
adamantine
at a standstill
cast-iron
dour
firm
flintlike
flinty
frozen
granitelike
granitic
grim
hard
hard-core
immobile
immotile
immotive
immovable
immutable
implacable
impliable
inductile
inelastic
inexorable
inextensible
inextensile
inextensional
intractable
intractile
intransigent
iron
irreconcilable
irremovable
irresilient
lithic
lodestone
magnet
marblelike
nonelastic
nonstretchable
obdurate
obstinate
pat
petrified
petrogenic
relentless
rigid
rigorous
rock
rock-ribbed
amenable
compel
emotionless
gratify
inadmissible
incompliant
outspoken
repellent
soft
staunch
strenuous
tenacious
thunderstruck
unanswerable
undistracted
unelastic
unforgiving
unmanageable
unreadable