Looks more like some kind of mineral build-up from the water. Could try CLR or a pumice stone very lightly on the residue part.

I agree, this is a mineral build up so try the CLR but you'll have to leave it a while and maybe repeat. You'll also need to get all the water out and the only way to do that is to turn the water supply line off behind the toilet and then the tank will have to be empty then you can proceed to get all the water out of the bowl, you may even have to use a towel to soak remaining water out. A toilet wants to refill itself unless you turn off the water to it.

If you manage to get all the water out, first retry vinegar and see if it doesn't work being poured in straight, leave it a long time and try scrubbing again.

Is it possible that the finish is chipped off the bottom of the bowl? My neighbors have that same situation and the bowl is chipped. You stated that you feel texture through the bottom of your glove. I would replace the toilet.

Thanks everyone!

I have been able to remove mineral deposit around the faucets by soaking with a dripping wet, vinegar soaked strip of paper towel. The soaked paper towel helps keep the surface wet. I leave it for a couple of hours, keep dribbling more vinegar on it, and it scrubs off easily with a stiff brush. CLR or Lime Away ought to help too.

Thanks, sheilajoyce!

My toilet has the same problem but I haven't ventured to clean it yet. However, for heavy rust and mineral deposits on a sink, after trying every product mentioned above with varying degrees of success, I used pumice and it worked. Not the pumice used for scrubbing your feet (that didn't work at all), but a pumice stick sold at the hardware store. It's much coarser, and as you scrub, it kind of dissolves into a paste. It worked for me. Now off to the store to buy some cleaner for the inside of the tank. Ick.

If you have had a chemistry laboratory where you were taught how to handle acids go to the plumbing section of a big box and buy an acid. Muratic is less harmful to other surfaces if spilled but it stinks. Sulfuric is really nasty but will dissolve almost any thing of the sort pictured.

If you have not had a chemistry laboratory read the fine print on cleaners. Some will say HCl. Our dollar store has one with nothing else. To use this one drain the toilet, dry it and flood the bottom with the cleaner containing HCl. Let it set for as long as you can. Then clean with the brush or whatever.

If I encountered this, I would go to the Dollar Store and buy a bottle of The Works. Then I would turn off the water valve and flush, thereby reducing the amount of water in the bowl. Then I would pour in The Works and let it sit for several hours. So, the same as what Albert 135 suggested but with The Works. Or do the same thing with the ZEP.

Giving the product time to work is the key.