Hematite is iron ore and often comes in a greyish metallic mass that looks like solid bubbles and leaves a red dust (rust!) residue.  You are most likely to come across it as a silver, polished stone. 

It is the most effective energy that I know for grounding, and can also be used for protection.  It is an excellent help for the effects of shock, following accidents and operations, and can help to stabilise in times of extreme stress.  Hematite can give strength and support in challenging situations. 

I wear Hematite anklets when flying to help with Jet Lag.