Dark materials

...any hopes that the nature of [dark matter] would be quickly revealed by these first detections have been utterly dashed. The trouble is that dark matter appears to be different things to different detectors. It appears heavier in one detector than another; it appears more ready to interact in one experiment than another. In the most extreme case, it shows up in one instrument but not in another - even when both are made of identical material and are sitting virtually next door in the same underground lab...

-- from Dark matter mysteries