Can black jeans pass as formal?

I don't think so...

Nope. Casual chic to semi formal at best.

they can if it's all you got

They could if you pair them with a dressy shirt and fancy shoes. It all about how you style them

Depends on the event and situation. For business casual wear, probably.

No jeans are not formal wear darling I wish they where cause I love them I don't know how formal formal is that your asking this but you could try the black jeans (only if there brand new real nice and back) a sports jacket and shirt no tie and I have no clue about the shoes

I'd say that it depends on the event and what other people are going to wear.

Typically I'd err on the side of caution and not wear them if in doubt.