Richard, the grains of diamond become rounded. I've heard people refer to this as "breaking in." I call it "wearing out" because after it happens the diamond stones don't cut like they used to or as quickly as, say, ceramic waterstones. The diamond stone will last virtually forever but it will only cut quickly, like a diamond, for a relatively short period of time. Since it requires no lubrication (waterstones require water) and no maintenance it would be the perfect abrasive except for the cost and relatively short longevity. Remember industrial diamond isn't as hard as natural diamond. In fact it's pretty close to the same hardness as zirconium oxide (the ceramic used in knive blades and waterstones.) Take care.
