Hemitrope

[Gr. hem i, and trepō, I turn.] Hemi tropal; half-turned round. -n. That which has an hemitropous structure. (Crystal log.) A term applied by some crystallographers to what are usually called twin crystals , from their being generally conceived to result from the cutting, as it were, a crystal in half, and then turning one of the halves half-round upon the other. The plane common to the two portions of the crystal is called the twin-plane. These crystals are often distinguished by the presence of notches or re-entering angles.