Soul Stone

Sell value
30 Gold

What drops it

 * Shiro'ken

Common crafting materials

 * 3-4 Granite Slabs

Rare crafting materials

 * 1 Lump of Charcoal

Testing
In a trial of 50 Soul Stones (1500 gp) salvaged using two Superior Salvage Kits (2 x 400 gp), 162 Granite Slabs and 6 Lumps of Charcoal were produced. The value of them as salvage or merchant sales depends on the value of granite slabs. If granite slabs are 140gp or more (16 x 140 gp, less 800 for kits = -60gp, plus whatever the charcoal brings), then it is probably better to "salvage & sell" rather than sell. In every case, if you are going to use granite slabs (a key ingredient in Powerstones of Courage), it's better than buying by far.