Dear Jan, Dear Paul
 
I've read all your comments. I have quite a problem too. When I donate
land-shells as Mediterranea shells to schools for their collection, teachers
will ask me for a value of a shell getting from me or what they just have
in old school collections. For me it's depending - as I don't collect only
gems, but for scientific purpose (or also very fresh dead specimens) -
from the work I have with the shells. To select out from detritus, mould, etc.
cleaning, classify, to be full of datas, etc. So it seems  1 dollar less, two dollars for a most common species to much, as Jan sayed. A shell will during several hundred years, if it is a good (now not in sense of qualities good, fine of gem) or not easy to break, or just very fragile from nature, otherwise if you sell a shell for one dollar you can't drink a cup.of tea or coffee for it. Otherwise it looks better if you donate a half dozen of commom shells not for 1 dollar, but worth as 6 dollars. For very rare shells the price in a list seems always to be too high, when a shells costs about 3000 dollars. There should bei a limit, but I don't know how much.
And for common shells not less than 1 dollar, therefore a shell seems to be worth nothing. But also the common,  small, unspectacular ones are worth
Please think what time a shell need to grow, when you drink a coffee,
which maybe costs 2 dollars within a few seconds.
Please let me know your opinions.
thank you
Helmut Nisters