i have 2 1975d Penny's and they look there made of different material and one look like it has a d mint mark stamped over in other new here so thank you for the help
The Mintmark looks like damage. Circulation wear. Looks like a normal copper cent to me. Normal environmental toning with change the appearance over the years.
The MM might have some contact marks, but there is no error there. The first coin is darker due to where it's been - same metal as the other 75-D. Coins don't always circulate exactly the same - some become darker due to other factors once it's been released into circulation.
A mint mark cannot be doubled, just re-punched prior to 1991 as they were applied to the die by hand and were not a part of a die prior to punching them.
