25K gold is audiophile approved 24K gold. You get to charge more over spot for it.

I think you are probably right about the six nines copper kinda thing.

Uh oh:

http://www.madisound.com/cgi-bin/index.cgi?cart_id=1539839.2138&pid=1472

Yes. "Spot" is "cash" or "good delivery." "Three nines fine." It is the delivery specification for the futures contract at the Comex (100 oz bars) or London (400 oz bars).
24K is a jewelry spec and is less fine than three nines fine. 24K is undeliverable on any major exchange in the world. 25K could be 6 nines, a figure of speech that simply means "purer than 24K." Or it could be 3 nines. Gold is easily alloyed with Rhodium, Platinum, Copper, or silver, so I guess the key point is not whether it is 99.999 or 99.999999, but what elements are alloyed with it beyond those last 3-6 decimal places. Anybody out there know? Mikey?

Shouldn't Mike Fremer be answering this ?

OK, question answered.

Typo.

Either that, or Clearaudio completely ignores the quality of gold Clifton tells us about and uses crappy old 24K gold in their 8,000 dollar "Goldfinger" cartridge.

Goldfinger cartridge

I'm betting typo for Mr. Fremer's review of their 2,000 dollar Concerto.

That 25K had me going there for a minute, though!

I wonder if Ian Fleming's estate receives any royalties from Clearaudio for every Goldfinger cartridge sold?