混じる

1. Origins, structure, and basic meaning

• Structure: 混じる is read まじる and describes something being or becoming mixed into something else.
• Basic usage: It applies both to physical mixtures, such as small shells in sand, and to regional expressions appearing in someone's speech.

2. Common pitfalls and similar expressions

• Particles in a mixture
  • In 砂に貝殻が混じる, が marks the shells being mixed in, and に marks the sand containing them.
• Mixing something
  • 混ぜる describes someone mixing things. 混じっている alone does not establish who deliberately mixed them, if anyone.