[TXnMA]

"Walking over hard black goo in spots that had oozed up through the sand. The site had been used by Morton Thiokol as a disposal site. I always wondered if this black crap was what they had made the gaskets out of?"

~~~~~~

No.

In all likelihood, the "black goo" was thiosulfide rubber -- the actual fuel in the solid propellant -- to which Thiokol added ammonium perchlorate as an oxidizer.

Then, they filled the rocket casings with the goo and vulcanized it in place in giant autoclaves...

The vulcanized rubber+oxidizer solid propellant looked like black, rubber shoe heel material. Thiokol engineers would demonstrate the precision of their fuel/oxidizer mix by lighting a small cube of it atop a white, glazed ceramic tile -- and showing that there was zero residue (not even discoloration) left...

~~~~~~~~~~~

You were walking on un-vulcanized (probably raw, without oxidizer) solid rocket fuel, itself.

[TXnMA]

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