Summing up this dragon, it's like a mish-mash of the amethyst and obsidian (Legend of Sardior bestiary) dragons, so giving it both Earth and Fire elemental subtypes is cool. In fact, I'd place it rather than the obsidian dragon as the aberrant gem dragon of Faerûn, inasmuch as the Realms have three aberrant metallics (mercury, steel, and the unofficially converted electrum), and two aberrant chromatics (brown and the Raurin/Mulhorandi yellow); and beljuril gems are found in Faerûn. The amethyst inspiration is slightly stronger than the obsidian, since it's a kineticist specialist.
I think we can add rules similar to starvation if the dragon doesn't convert energy into hit points.
Seismic Metabolism (Su): Beljuril dragons derive sustenance from seismic energy, and they must stay in a seismically active environment to remain healthy. They don’t actually consume gems and minerals, but surround themselves with them by filtering the seismic energy need to survive through the crystalline structures of the stones. Beljuril dragons are surrounded by an effect similar to energy adaptation, except that it extends to a range of 10 feet per age category of the dragon and it assimilates only effects from earthquake, stomp, and other earth-based effects, as well as fire effects directly related to earth such as lava flows. Fire from other sources is not assimilated. Any earth- or fire-based effect that deals damage heals 1 point of damage for every 3 points of damage it would otherwise deal. If the amount of healing would cause the dragon to exceed its full normal hit points, it gains any excess as temporary hit points. A beljuril dragon that does not convert energy into hit points equal to twice its age catergory [per day?] suffers the effects of starvation as described on page…
We can give the explosive gem at adult age like the amethyst:
Explosive Gem (Ps): Once per day, an adult or older beljuril dragon can spit a green, violet, or blue crystalline lozenge up to 75 feet away with pinpoint accuracy. This lozenge converts fire, light, or sonic energy into electricity (in a manner similar to energy conversion, except that it is manifested as if it was a 3rd-level power). It disintegrates on impact, dealing 1d6 electricity damage per manifester level in a 20-foot burst (Reflex save for half damage), but 10% of the time it breaks apart into 1d6 fist-sized beljuril gems worth 5,000 gp base value. (Beljuril gems are described in Magic of Faerûn.)
Finally, we just need to this footnote to the Table: Beljuril Dragon Abilities by Age.
*Beljuril dragons manifest powers as if psions with Psychokinesis as their primary discipline.