text: Terrestrial sediments also contain micrometeorites. These have been found in samples that:
  *Have low sedimentation rates such as claystones and hardgrounds
  *Are easily dissolved such as salt deposits and limestones
  *Have been mass sorted such as heavy mineral concentrates found in deserts and beach sands.
  The oldest MMs are totally altered iron spherules found in 140- to 180-million-year-old hardgrounds.