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.
 
7 - 4" x 1.25" x .75" - $6.00
8 - 2" x  2.25" x 1.25" - $7.00
9 - 2" x 1.25" x 1" - $6.00
10 - 2" x 1.25" x .5" - $5.00
11 - 2.25" x 1.75" x 1" - $5.75
12 - 2.5" x 1" x 1" - $5.00