The formation of rubies and sapphires is an unlikely event.
This Discovery article from 2003 gives a description of the formation of corundum deposits in marble (metamorphic limestone). Just before this article was written, I was taken to a marble deposit near Phrae, Thailand. I was told that, at one time rubies had been found there. As the article states, these deposits were likely a result of the collision of the Indian plate with the Eurasian plate. The article goes into more detail.
Greenland contains some of the oldest rocks on earth - 3 billion years old
Consider the gold/diamomond formations in South Africa
which are about 2 billion years old