It would be hard to explain why including gems on my equipment tables is difficult. It isn't so much that I couldn't make a list of gems, with price and availability ... it's that adding a different size for each type of gem gets to be inconveniently long.
Desireably, I long-since decided, I could put up a random list. That too proved difficult, what with accounting for availability and size, to make a generation table that was both practical and interesting.
I hope I've done it. I worked all day today on it, and I'm happy with the result. I can't show it as one table, however, since ... well, its randomly generated. So all four of the below images are individual manifestations of the result. A party, to sell their gems, has to get a little lucky with the local demand.
I don't imagine this will mean much to the gentle reader. But I get a warm feeling.
No doubt some will ask why there's a price to buy if there are none available. Well, it's partly a general programming issue (I don't feel the need to wash it out), and at the same time it does give an indication of the mark-up the store is getting over the supplier.
I trust there's enough there to give a general idea of the availability of gems for sale. The weights are based on the mass not only of the size of the gem, but also of the specific density of that particular gem as opposed to others; amber, for instance, has a low specific density, so a plum-sized amber weighs much less than a plum-sized cat's eye.
It will also be noted that the gems are much larger here than they would be in the real world. That's intentional. Somehow, I prefer that gems be the size of cherries, almonds and plums rather than tiny little chips or pin-heads. I could adjust all my prices and availabilities to make the world fit the modern truth, but this just seems more appropriate for a fantasy world.
I've learned a lot from this. I need to try to adapt that to jewelry ... which is bound to be much, much harder. Also, I'll have to repost this table when adding other things a lapidary does beyond providing the stones. But I'm tired and I wanted to post this, after a full day of continuous programming.