The rubies themselves were of little value Casandra displays a ruby necklace to Daciana, although she is not a trained jeweler, she has seen treasure hordes in the past and knows this gem would be lucky to fetch 100 gold. There is a magical nature to them but only when worn by an amazon AND a worshipper of one of the trinity, they allow telepathic communication. For an amazon of, say, Glendira, they don't work, or for a human follower of Tishtina, again, nothing. So for the dwarves, they weren't worth anything and they weren't interested in selling them, to anyone, they had locked them away so they weren't even being bartered. We only found out about them because of a dwarf who had discovered their hiding spot and the ancient legends that had caused the dwarves to lock them away centuries before the prophecy was even written. From what he told us, they would not have even entertained the thought of selling them to us, many of their highest nobles didn't even know they existed.

(The dwarves of Iron Hall are entirely lawful, most L/G with a smattering of L/N. In the past, the dwarves shipped their gold and gems through the amazon lands to Matalla to be shipped around the world and sold, with the proceeds coming back through Amazonia on their way to the dwarf lands. The amazons took no percentage from this, only allowing passage for free.)