The Gem of Taron

Back at the Carousel Boutique, Rarity, overjoyed with her find of the brilliant gemstone, hastily began to take measurements of Twilight's dress,  making sure the gem would fit onto the dress. Amazingly, the gem was a perfect size, no need for cutting. Excitedly, Rarity began the process of attaching the gemstone to the dress, making sure it was fitted tightly.

After the work was done, Rarity admired her handiwork. The stone completed the dress, it was one of her finest creations. The white of the dress offset by the shining deep red of the stone. It was perfect. Almost too perfect. Rarity was, unadmittedly, a little wary of the stone.

"It seems a little too coincidental that I happen upon a perfect gemstone in a time of desperate need" Rarity said to herself, pacing around the boutique floor. It was rather late, and Sweetie Belle was tucked up in bed, so no worry of anypony interrupting her thoughts. "I should see if I can find out any information on this stone".

Rarity had a knowledge of gemstones far beyond anypony else in Ponyville, maybe even the whole of Equestria, so her discovering a gemstone that even she had not seen before was concerning. At first she thought the stone to be a simple ruby, but it became evident it was so much more than that. It radiated such a powerful aura, it was definitely more than just a ruby.

Rarity searched through the books she owned about gems and minerals. If she didn't know of it, there'd definitely be something in her books. But no, as much as she searched, checked the books from cover to cover, there was nothing resembling this perfect gemstone.

"As much as it pains me to use a gemstone without knowing it's origin, I'm afraid I simply must use it" Rarity conceded, knowing this gemstone was her only chance of completing this dress, lest another journey to the mines in the blackness of night commenced. Rarity, being the perfectionist she was known to be, gave the dress a final once-over, ensuring every detail was perfect. The white of the dress at the front, slowly transitioning into a dark purple at the back, the diamonds around the base contrasting the darker colours, it was surely a dress fit for a princess. Satisfied with her work, Rarity retreated to her bed, the thought of the gemstone still on her mind. Once the pony had drifted off to sleep, a low eerie whisper resonated from the gemstone.

"Foolish unicorn, you do not know what you have wrought. When the Princess wears the dress, I shall take control of her, and take Equestria for my own!"