It turned out to be an extremely good hyalophane fourling with Carlsbad twin attached.
The result is two types of fourlings. Some authors (Grammaccioli, 1975) use the terms "Manebach-Baveno" and "Baveno-Baveno" fourling, whereas others are not aware of the two types (Baric, 1972; Linck, 1923; Philipsborn, 1967; Ramdohr and Strunz, 1978; Roesler, 1980; Schwarzman, 1977; and Weibel, 1990).
Typical of both fourling types are secondary Manebach twins positioned around the fourlings.
This type of fourling is present in crystals up to several centimeters, which are combinations of alternating and narrowing M, T, P, x, d and z forms.
Such morphology can be described by the translation of this fourling in the direction of its common fourfold axis.
Two secondary Manebach twins can be formed at the points, where the fourling is broken in the (021) twinning plane.
This structure is defined by the two possible combinations of two types of fourlings. Assuming that a crystal could be broken alternately on both sides and rehealed, a fourling with a double conical form would develop.
This type of double fourling is characterized by secondary Manebach twins that are symmetrically intersected by (010) and (100) fourling planes of symmetry.
This type of double fourling is characterized by the two different apex structures: one is of the (001)-fourling type and the other of the (010)-fourling type.
The situation is completely opposite with the (010) fourling, where its (010) faces are protruded with (001) and (101) faces of secondary Manebach twins.