The Collaborative International Dictionary of English v.0.48:

Flinty \Flint"y\, a. [Compar. Flintier; superl. Flintiest.]
   Consisting of, composed of, abounding in, or resembling,
   flint; as, a flinty rock; flinty ground; a flinty heart.
   [1913 Webster]

   Flinty rock, or Flinty state, a siliceous slate; --
      basanite is here included. See Basanite.
      [1913 Webster]

WordNet (r) 3.0 (2006):

flinty
    adj 1: containing flint
    2: showing unfeeling resistance to tender feelings; "his flinty
       gaze"; "the child's misery would move even the most obdurate
       heart" [syn: flinty, flint, granitic, obdurate,
       stony]