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THE METAL-BENDERS” by JOHN B. HASTED

A simpler type of break is the cleavage that occurs when a single crystal of metal is sheared. The fracture surface then follows one of the crystal planes, and can appear to be planar over quite large areas.

Paranormal fractures of silicon and similar crystals have been reported in experiments with Uri Geller and Jean-Pierre Girard, and I have myself observed cleavages of single crystals of zinc by Graham P. and Andrew G., and of silicon crystals by Stephen North.  The zinc crystals were 1-in.-long rods, about the thickness of a pencil, and Metals Research Ltd had prepared them with their 0001 surface perpendicular to the axis of the rod.

Each of the following types of paranormal crystal cleavage has been brought about by the observed stroking action of metal-benders:

1 The crystal cleaved straight across, leaving mirror-like 0001 cleavage surfaces on each piece. One piece remained between the thumb and forefinger, and the other simply dropped off the end, at some distance from the hand.
2 An 0001 cleavage crack developed part of the way across the length of the crystal, within a few millimetres of the end, but, again, beyond the end of the thumb and forefinger.
3 A flake of 0.1 mm thickness hinged upwards at an angle of about 45° from the end of the crystal and remained in position, although it was very delicate.
4 A slight kink developed in the crystal, but without cracking.
5 Grains of about 1 mm in size parted from the crystal, leaving the edges badly scarred. An 0001 plane crack also appeared.
 

It is true that even at room temperature these zinc crystals will deform and cleave fairly easily. Three-point loading of a 7 cm length with 4 kg causes some yield, followed by a cleavage. A blow with a sharp blade mounted on a weight of 500 gm dropped from a height of 15 cm also causes cleavage. Nevertheless the handling of the crystals by the children was observed by me and seen to be much more gentle than this; I hesitate to fault my own handling, or that of Metals Research.

In paranormal cleavages the surface of action presumably remains planar over a macroscopic region, and acts only in a certain crystal plane, in this case 0001. But a crack will propagate along a plane, even though the force is locaised at the edge of the crystal, so that it is not clear just how far the planar surface of action extends. In the fracture of aluminium strips bonded by epoxy-resin, the action is also planar at the metal-epoxy interface; one of the metal strips might be imagined to experience dynamic strain and the other not. These bonds are very much stronger than in the zinc crystals.