Is gorgeous an adjective

Yes, it is. It's a Word that describes a noun.

One quick way to check if something is an adjective is to make a phrase with an article, then the Word in question and then a countable noun.

e.g a gorgeous woman / a gorgeous painting.

Try to use a noun that would go with the adjective in question because you're basically asking yourself the question "Does it sound right?" A phrase like "A gorgeous Pizza" while grammatically correct sounds a little weird.