Purple shard

Purple shards are a type of shards used to fuse and evolve gear. Unlike red, blue and green shards, purple shards are only used to evolve a piece of gear to its stronger form, but not for normal fusing. Additionally, it can only be obtained by shattering 3-star gear (prior to evolving; shattering 2-star gear evolved into 3-star will only give back the one shard used to evolve it in the first place when you shatter the last piece). It can also be obtained randomly from the wheel before every match in Survivor, which has a chance of awarding a single purple shard.

It's relative abundance and low usage makes it a "junk" shard, especially for more experienced players.