Final answer:
The sentence is a metaphor comparing music to waves washing over the mind.
Step-by-step explanation:
The sentence 'Long blue waves of music washed over my mind' is a metaphor because it is comparing the waves of music to a physical action of washing over something, which is not literally possible. The metaphor is being used to describe the powerful and immersive experience of listening to music.
In this metaphor, the music is compared to waves, emphasizing its flowing and rhythmic nature that can envelop one's mind.
Learn more about Metaphors and Similes