There have been many news reports about 1970 US Quarters that are worth tens of thousands of dollars. The news reports show pictures that need lines drawn on them so you can see what they are trying to show you. Truth be told, they are very hard to tell from a normal quarter.
Here is one quick trick to help you know if your coin is a quarter struck on a US planchet or a Canadian planchet. As you can see in the picture below, the US and Canadian quarters are the same size and measurements. But if you look at the second picture you will find that the EDGE of the coins look very different. That is because the US coin has a ”sandwich” appearance, but the Canadian coin has one color to it.
What this means for you is that if your coin has the sandwich copper look, it is NOT the error coin. If it looks like it is all one color then it possibly is on the wrong planchet.