Funny - I never thought about using the "Stock" option.

You and sarge are right - there would be categories (e.g., "Sapphires") but the quantity of each sapphire would be limited to one item - since each is unique it would sell out as soon as the first one was purchased.

I've pondered the idea of what happens if person "A" selects a stone, starts to fill out the order, and doesn't complete it very fast. Meanwhile, person "B" selects the same stone, is fast with payment, and beats person "A".

That is probably a future problem. To start out with the volume will likely be low.