Some ideas for the mineral exchange.

1. When selling a piece too small, could it be told what the minimum
size is so we won't bother trying a hundred times over the years.
(add this to the help plaque too)

2. Add some sort of 'recycling' service that pays some small amout
per kg for every mineral type. I mean, when a newbie like me finds
a piece of mineral, the first place he will head to is the mineral
exchange. And currently the newbie (me) will be disappointed every
single time.

3. For merchants, make the store only accept divine refined materials.
And, since the mineral exchange is not a place to store your minerals
or to get them quickly cutted into desired chunks, prevent buying of
own materials.

4. Because of point 3, now you can get rid of the horrible buying
syntax of:
'buy any 2 good refined nullium for 666'
and change it to:
'buy 2 nullium for 666'.
C'est beaucoup plus jolie comme ca, n'est-ce pas?

5. I had more but I forgets.