Black Stuff On Side Of My Cats Mouth

When I was brushing my cat Abby last night I noticed  some sort of black stuff that looked like coffee grounds on the side of her face just under the opening of her mouth.  I tried to rub it off with my finger and it appeared to be breaking up and falling out, almost like flaking skin or dandruff on a human.  Could this be Feline Acne and if so, how do you treat it?  Is it serious.  I never realized all the little health issues with cats, my cat is nine years old.  Thank you for your help.