Polysynthetic twinning

Polysynthetic \Pol`y*syn*thet"ic\
   (p[o^]l`[i^]*s[i^]n*th[e^]t"[i^]k), a. [Poly- + synthetic.]
   Characterized by polysynthesis; agglutinative.
   [1913 Webster]

   {Polysynthetic twinning} (Min.), repeated twinning, like that
      of the triclinic feldspar, producing fine parallel bands
      in alternately reversed positions.
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Twinning \Twin"ning\, n. (Crystallog.)
   The assemblage of two or more crystals, or parts of crystals,
   in reversed position with reference to each other in
   accordance with some definite law; also, rarely, in
   artificial twinning (accomplished for example by pressure),
   the process by which this reversal is brought about.
   [1913 Webster]

   {Polysynthetic twinning}, repeated twinning of crystal
      lamellae, as that of the triclinic feldspars.

   {Repeated twinning}, twinning of more than two crystals, or
      parts of crystals.

   {Twinning axis}, {Twinning plane}. See the Note under {Twin},
      n.
      [1913 Webster]