What mineral is nonmetallic and black and can be scratched by a penny?

The mineral you are describing is likely talc. Talc is a nonmetallic mineral that is typically black in some varieties and has a very low hardness of 1 on the Mohs scale, allowing it to be easily scratched by a penny, which has a hardness of about 3. Its softness and slippery feel are characteristic of talc, making it commonly used in products like talcum powder.