The margin of the vein is distinct. A distinction between wall rock and veins is difficult to make. In both movies, opening is initially horizontal and then oblique. This opening history cannot be determined from the shape of the stretched crystals, which only reveal the average opening direction over the whole growth history. All these terms may be confusing if they are not fully and accurately defined and consistently used by different authors.
Syntaxial veins grow from and in continuity with the wall rock inwards.
At the growth surface of an antitaxial vein, growth is in one direction only and hence they can be termed unitaxial, while growth in syntaxial and stretching veins is from both sides of the growth plane and these veins thus show bitaxial growth. What is clear, is that these veins are unitaxial, as growth is only in one direction at the growth plane. A syntaxial vein has only one persistent growth plane. It is clear that syntaxial, antitaxial and composite veins can provide detailed information on the progressive sequence of conditions under which these veins formed. These veins are elongate blocky or fibrous and the direction and curvature of the crystals indicate the kinematics of deformation and the orientation of the stress field.