Rocks of Mechanical Origin – Rudaceous        Sedimentary particles of mechanical (terrigenous) origin are classified according to their size. Particles larger than  2 mm  constitute  gravel  (Latin-rudite), those between  2 and 1/16 mm  constitute  sand  (Latin-arenite), while those  finer than 1/16 mm  constitute  silt and clay  (Latin-lutite). Accordingly, sedimentary rocks of mechanical origin are classified broadly into three groups:  Rudaceous, Arenaceous  and  Lutaceous  (aka  Argillaceous ). Rudaceous Sedimentary Rocks  (Conglomerates and Breccias) Unconsolidated sediments coarser than 2 mm are grouped under the term gravel. Indurated gravels are called conglomerates. While the particles constituting a conglomerate are essentially rounded, a breccia consists of gravel-size clasts which are angular. The term rubble is applied to an assemblage of loose angular fragm...