polysynthetic twinning

Wiktionary

1. n. geology A type of contact twins where the composition surfaces are parallel to one another.

GNU Webster's 1913

1. adj. (Min.) repeated twinning, like that of the triclinic feldspar, producing fine parallel bands in alternately reversed positions.
2. n. repeated twinning of crystal lamellæ, as that of the triclinic feldspars.