FANMADE The heart-shaped Fire Ruby

The Fire Ruby before being made into a necklace

You know, when I was watching the episode called "Secret of My Excess", the Fire Ruby made its first appearance as a gem istelf. It used to be Spike's, but he gave it to Rarity. She was so thrilled she had the same gem and I saw her do the Pinkie Pie jump taking the Fire Ruby with her. None of us people never saw her make a necklace out of the same gem and a dash of gold. And as I'm thinking, she tried it on herself. I can also see it in her flashback in "Magical Mystery Cure". My question is, why do some things change? My eyes can see the answers of some changes. Rarity is always determined to wear the Fire Ruby necklace which is exactly a piece of jewelry.