1997 D Dime Duo Clad Layer Missing

On the reverse the rim is showing some silvery color as well as some high points on the torch and both branches.
On the obverse, same thing on the rim, I also think that the grayish color is from the cladding.
On the edge, I see some dirt stuck in the reeds.
I think this coin spent some time in dirt or something similar.

I'll go for environmental toning at this point.
Maybe some of the other experts here can have something to say as well.

Enviromental damage and worth 10¢
John1

When a clad layer is missing, the coloring will be much more like copper such as the dime on the left which is the one missing the obverse clad layer so you can better see the difference in coloring which may help you (and others) in the future when looking. Yes it can be partially missing as in this link as well https://www.PCGS.com/news/missing-c...-error-coins



A missing clad layer is a coin that has one of its outer nickel layers missing from the copper core. As a result, the typical missing clad layer coin will be copper on one side and nickel on the other. It also will weigh roughly 15% less than a normal coin. This happens on dimes, quarters, halfs, and dollars since 1964 but not nickels. The weight will typically be different as well, we were discussing that recently here http://goccf.com/t/443739#3827140

The alloy used for nickels and the outer clad layers on dimes, quarters, and halves are susceptible to environmental damage also resulting in a darker appearance. Unless you are getting them from mint bags or rolls it would be hard to know exactly what its been exposed to during its circulation. They can also develop toning. Here are some of the things I've read that can cause a coin to tone dark or can cause a coin to turn a variety of colors, from deep grey or black to mottled or speckled.

Experimentation with acid, or just normal corrosion
Burial in the ground
Being tossed in a water fountain
Exposure to intense heat, or very cold temperatures
Storage in a paper envelope, PVC plastic, or open-air case
Contact with caustic chemicals or fumes, such as sulfur or gas
Sitting in a warm and humid environment for long periods of time
Placed in old fashioned coin folders or albums can also cause toning, potentially attractive, with colors ranging from light blues and pinks even to rainbow colors.

Agreed that the clad layers are present. This is a coin impacted by environmental toning/damage.