This is what the pyramids used to look like. They were covered with polished white limestone and had a peak made of pure gold.
(lemmy.today)
Just looked on wikipedia and they say
"... and were sometimes covered with plates of copper, gold or electrum."
(electrum is an alloy of gold and silver IIRC)
https://en.wikipedia.org/wiki/Pyramidion
Which makes a lot of sense, gold was and is very expensive