The Crystal Shards are objects that appear in Sonic Boom: Shattered Crystal. They are fragments of the Lost Crystal of Power which the Ancients shattered into several shards and then hid away to keep them out of the grasp of Lyric the Last Ancient.
One of the objectives in Sonic Boom: Shattered Crystal is to locate all the Crystal Shards.
The Crystal Shards are hand-sized purple (light blue in the in-game comic) shards with a rough surface. Each containing a fragment of their aggregated form's power, the Crystal Shards can be harnessed to warp reality to some extent, like when the Ancients used them to imprison Lyric.
While the shards are powerful enough for the Ancients to deem them dangerous, they do not seem match up to the Lost Crystal, even when used together, since the Ancients were only able to imprison Lyric temporarily when using all of them.
Sonic Boom: Shattered Crystal
When the power-mad Lyric the Last Ancient was on the verge of obtaining the Lost Crystal of Power which would give him omnipotence, the Ancients opted to destroy the crystal, shattering it into forty Crystal Fragments which they used on Lyric to imprison him. However, the Ancients knew it was only a matter of time before Lyric would return, so they scattered the Crystal Shards to prevent the Lost Crystal from being reassembled.
Lyric eventually escaped 5,000 years later and started searching for the Crystal Shards. Meanwhile, Amy Rose had discovered a secret ancient language and manuscript detailing the history and whereabouts of the Lost Crystal of Power's fragments. As such, Lyric kidnapped Amy to probe her mind for information on the Crystal Shards, but Team Sonic put a stop to his plan. During their journey, the team also found all the Crystal Shards and reassembled the Lost Crystal.
One of the side quests in Sonic Boom: Shattered Crystal is to collect all forty Crystal Shards which are hidden in the adventure levels. Each level holds five shards, each of which can be collected by opening a spherical silver and red container with a Crystal Shard inside it. These containers break when touched and can be targeted with the Homing Attack. Collecting all five shards in a level will unlock a Sonic Badge. After obtaining one, the player can bring any shard to Sticks' Burrow to reassemble the Lost Crystal. Additionally, the shards used for the restoration will fill in various spots on the crystal, affecting the way the top screen looks during loading times.