((Prompt: Tell me about a bottle.))
It had been sand once, as all glass was. Once, it had been a million grains whipping in the wind across the endless dunes of Saddle Arabia. A glassblower had scooped those grains up, melted them down and shaped them into the bottle it was today. It had contained water from a blessed spring once, and was given as a gift from a traveling merchant to a member of the nobility in Canterlot. It had been emptied of its spring water within a few decades, but the bottle itself had been kept for generations for its fine craftmanship.
Eventually, the noble house had run out of heirs and bequeathed the bottle, along with many of their possessions, to Celestia. It lay in the palace for many years, untouched, until a curious filly discovered it while browsing ancient relics with her princess. Celestia gave the bottle to her student as a gift, and so when Twilight Sparkle moved to Ponyville, so too came the bottle.
Now it stood by itself on a bedside table, currently serving as a reminder of how desperately little ponykind knew about dragons.
Deep tooth-marks scored the lip of the bottle, jagged scars running parallel along the glass. Dragons were not mammals; they lacked the capacity to suckle on something like a foal would for its mother's milk. When Spike had fallen too ill to chew his food, Twilight had thought to feed him medicine from the bottle, but because he was unable to drink from it, most of the medicine had ended up on the floor.
Which had been for the best, for what little medicine that had made it inside had had the opposite of its intended effect. One side of the bottle was blackened and melted from the noxious flames he had spewed as the medicine had only served to upset his stomach even further.
Residue from the ground carbon mixture Twilight had stirred the medicine in remained stuck to the inside of the bottle, glittering in the afternoon sun. She did not understand; chemically speaking, it was the same as the diamonds that had always seemed to bring life to his step and a sheen to his scales. It was simply derived from an easier to find and easier to process form so that she could feed it to him without requiring him to chew. Twilight possessed no means to grind up actual diamonds, for they were too hard.
Twilight's eyes shifted from the bottle to Spike. He lay in his little bed, groaning between labored breaths. He was uncomfortable to even be around, as a dragon's fever was hotter than a pony's by several orders of magnitude. The edges of his blanket began to fray and sizzle, and Twilight knew she would need to find a more fireproof place for him if it continued.
Her eyes slowly slid up to the globe on the shelf above. It was one of the things that had been part of Spike's collection the day he had undergone his spurt of greed-growth. Now, it slowly turned on its pivot, showing her a profile of Saddle Arabia as it came around. A thought formed in her head.
Perhaps it wasn't the mineral content that Spike fed on at all. After all, during his greed-growth, he had not really eaten any gems at all, yet he had grown to a monstrous size in a matter of minutes. The dragon had grown with his hoard.
She glanced back at the bottle. Even ruined as it now was, the glasswork was something that no longer existed in Equestria, making it one of the most valuable objects in the library. She seized it in her magical grasp. Maybe... just maybe Spike didn't eat gems because they were gems, but because they had value. If a dragon's life force was tied to the value of its hoard, rather than the physical content of it, then it followed that more expensive things would naturally be more nutritious.
The glass had once been sand, and now was sand once again as Twilight Sparkle pounded the bottle into dust. She whipped it into a slurry and fed it to Spike by spoon. Physically, it was little more than wet sand, but fiscally, it was the remains of the most expensive thing she owned.
Spike swallowed weakly. A few grains of priceless glasswork stuck to his cheek as his eyes fluttered open. “T-Twilight?”