I watched an anime around 2008-2010. In it, the main characters use crystals to summon monsters to fight.
All I can remember is the main characters' appearances:
- one was a red hair male middle age
- one teen blond guy
- one teen girl
Probably Huntik, an American-Italian cartoon aired between 2009 and 2012.
Here's a sheet with all Titans and their summoning amulets:
Throughout the series, the kids fight against the evil Organization, whose goal is to rule over the world (such originality !). The Organization seeks a huge, legendary-like Titan to ensure their domination. So basically, they're like villainous Pokémon teams, but without the catchy name.
Plagiarising my own answers to Animated show with character who has a stone that summons creatures and Fantasy cartoon show aired in India around 2005-12; main character searches for his father. Involved magic rings
Could it be Shin Shirayuki-hime Densetsu Prétear? I believe it involves using crystals in battles with monsters.