Figure above :  Snow crystal of the above Figures.
In addition to the directions of fast growth (three pairs of opposite directions, green), corresponding to six fast-growing prism faces (perpendicular to these directions) and represented in the crystal only by branches,  the directions (and only the directions !) of the six slow-growing (permanent) prism faces, that is, the permanent vertical prism faces, are indicated (black lines, drawn at an arbitrary location in the crystal). The growth directions corresponding to these face directions are (naturally) perpendicular to the latter.
As can be seen in the Figure, all six permanent prism faces are, with respect to their directions (and that is :  three directions), present everywhere in the branched crystal. They border the distorted hexagons, and there they are (vertical) faces.