Been in our surrent house for 10 months now. One of the earlier
'fixes' was to replace all of the old dark brown outlets(most were
painted) with white ones. Everything went smooth and I didn't find a
single outlet wired backwards or ungrounded.

present day...
I was changing some of the wiring in the garage and found 10-2 wire, no
breaker is over 20 amps. Simply disconnecting a wire from the fixture
caused the end to snap. Closer inspection revealed what looks like
copper-coated aluminum wiring.

Did they ever make such a thing?
The house was built in 75 and from all appearances everything has been
untouched since then except for one bathroom.
Are there any hard & fast ways to identify non-copper wiring from the
sheathing? All of the wiring in the house is romex, no bx.
If it is copper-coated aluminum what are my options other than never
sleeping again?