User blog comment:Lord Loss/Monster Hunter Theory... Blog/@comment-184.38.85.69-20120816205958/@comment-4775842-20120824134846

Rubies and sapphires and other gems probably form through the accumulation of impurities that the monsters take in (such as the toxins found in most predatory fish... including tuna and catfish). It even says this is what happens in the description for WyvernGold. I suspect the same thing happens for the rest of those objects. It's even possible that these gems are malignant to the monsters' health, like kidney stones are to us.