What do I have

[Henry2]

I believe it is a reale, it's dated 1770 and is about the size of a nickel, the edges have a design around them. The coin weighs in at exactly 4 grams. The pictures came out crappy so I tried to describe it the best I could.

 

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[Mackaydon]

You nailed it:
1770 1R (figure '1' on the opposite side of the shield form the letter 'R' (real); Mexico City mint (small 'o' over large 'M'); assayer's initial 'M' (afer the date); diameter should be about 20mm. The edge has a design of laurel leaves.
Don.........