my apologies to anyone who might have felt bothered by me starting a new thread on this..I do check previous posts to make sure I'm not asking the same, this time around I saw no comment on the matter and it makes sense: the google search above shows only one thread from about a week ago (besides mine, of course) with the same question and it does bring some light in that respect (thanks chodba!)
I can understand that if that same past thread was heavily replied to it may have felt as though a zillion forum users were posting the same from anew every time (??)
anyhow, going back to trading-related stuff: I'm puzzled because if the reason for such spikes are dark pool orders making a match and dark pool trades seem disabled on MtGox after the re-opening, how are those dark trades taking place? does anyone else have the capability to place trades on the dark pool? (there used to be a drop-down menu, I don't see it anymore)
Spikes are a bug, probably in reporting. No real trades are made at that price. Or even if they did, they are tiny and not representative of the market ( ie buggy code matched an order way the fuck away from the market price). I think you need to study up on depth of market and also get a better understanding for how trading works. The market price is the last sale made. It will reflect the lowest remaining ask or highest remaining bid on the order book immediately before the last portion of the trade was executed.
Go here for a nice graph:http://mtgoxlive.com/orders?oneaxis;volumeon