The Magic Circle spells have powdered silver as a material component. Since there is no cost listed, the cost is small enough to ignore it. Does anyone else get a headache thinking about this?
Well, if silver coins are made of silver, and it takes 10 silver coins to equal a gold one, wouldn't grinding up a coin of silver or two be negligible in a game where gold is the standard unit of wealth?
Here's a possible explanation:
It's a standard action to cast. You can't possibly lay out powdered silver neatly enough in a 10' circle in approximately 3 seconds. So the act of casting the spell must take your negligible amount of silver, and form a perfect 10' circle, a mere 1 or 2 grains wide. Adding it all up, it's still a decent amount of silver, but a spell component pouch has all manner of strange things in it. So any strangeness derives from the pouch.
I can dig it. I hate keeping track of silver coins on my character sheet. More often than not, when I have to spend money on anything less than 1g, I round up to 1g, just to save myself the few milliseconds of calculating it would take to write down the difference.
If it's copper, I don't even track it. I figure I make up the difference in rounding up with silver.
I think they wanted to evoke the general idea of a circle of silver that Magic Circles tend to make folk imagine due to literature and movies and things, without giving the spell a costly material component.
So they compromised by saying it takes silver- but not making you pay for it.
-S
Pretend it's salt.
Its ground up reaaaaaaly fine and you don't need to use a lot of it?
For casting purposes costs not counted in gold coins are considered negligible. Ball of bat guano and sulphur? You can get a pouch of that lasting for multiple castings for five gold coins - because the cost per casting is much lower than 1 gp it is considered negligible.
Compare that to bless water - the component for it is powdered silver. Five pounds of powdered silver per casting, in fact, which costs 25 gp. A significant amount when compared to small pinch required for magic circle.