joasis,
They are two different characteristics. Mineral stains may or many not be present in the living tree. Spalt is a step in the decay process. Spalting has distinctive black, spiderweb-like lines, usually following the annual rings. It is most noticeable in lighter woods like ash, cottonwood, maple, hackberry and white oak. I think it occurs in all species.
Timing is critical in that the more spalting, the farther along the decay process. You can still have solid wood with very fine spalting. As the spalting gets more prominent the wood around it may be doughy or soft. Solid wood, with spalting, will normally sell for several times more than a similar board without spalting. It is very popular with turners too.
