Black Tourmaline is grounding and protective. This is one of the crystals that I use in my protection grids.  Great to place by a door for protection.
 
If you want it to stand guard by your door, "plant" it in a pot with soil.
 
1 - 4.25" x 1" x 1.25" - $12.00
2 - 2.25" x  1.75" x .5" - $6.00
3 - 2.5" x 1.5" x 1.5" - $8.00
4 - 2.75" x 2.75" x 2" - $17.00
5 - 4" x 1.5" x 1.25" - $7.00
6 - 2.5" x 1.5" x 1" - $6.00