Tricky unique grammar

Just another note about the challenges of the English language. Why “a unique…” rather than “an unique…”?
When a “u” word is pronounced as though it begins with a “y” (yoo nique), it’s treated more like the consonant sound of the y.
So:
- a university;
- an umbrella;
- a usual day;
- an unusual day.
Thank you, the information was really useful for me!