Most pearls are traded by weight at wholesale.
Value (which is not necessarily price) is not just a function of weight however otherwise some extremely poor quality pearls would be extremely large and extremely valuable. Which they are not. Something very small but perfect will be of more value (and price)
Yup! The reason has to do with the pearl being a fully nacreous (heavy) pearl as opposed to a light pearl (gas filled). Gas filled pearls having much organic matter inside of them, sometimes being brittle too.
Here is a photo of one of these "Gas Giant Pearls" and you can see what I mean by this
Out of curiosity Douglas, can a gas pearl be stablized like, say, a mabe pearl is? In other words, can the cavity be filled with a resin so that the outer shell remains supported?
I don't see any reason why Resin wouldn't work. It would probably take a syringe and a reasonable size drill hole as it's fairly thick. It can also start to thicken up fairly quickly so you would need to work fairly fast. I'm guessing here a bit ... there are so many resins out there that im sure there is one that stays liquid longer than the one I use. There's also some shrinkage when it dries... worth an experiment on something inexpensive.