What is this stuff in my shower and how can I get rid of it?

There’s this black sort of spotted stuff in the corner of my shower. I’m guessing it’s mold or mildew but I can’t scrub it off, it’s totally hard and stuck to the shower floor! I’ve tried shower spray specifically for mold and mildew but it did nothing. What can I do?
Answers

clayton

Use a fine grit automotive rubbing compound. Can be purchased at any auto parts store.

Joe

Yeah, it's mold. Nothing for it but hard work and strong chemicals. Mix up a solution of about a pint of water, an ounce of liquid laundry detergent, and an ounce of chlorine bleach. Scrub away with a stiff brush until your eyes are watering and your lungs can't take it anymore. Take a break, and get back to scrubbing. Wear clothing you don't care about. Next time, don't let it get this bad before cleaning.