Weird Canonical Tag Question

[Michael_H]

I'm having trouble getting an answer to the following, and shopify tech support sent me to the forums to seek help. It's kind of a unique question about canonical tags. Our online store sells large amethyst geodes. Each one is one-of-a-kind so each one gets its own listing in our store, however they all share the same lengthy product description, except for a few details like size and weight.

Here are a couple different examples of the product description so you can see what I mean:

https://cosmiccuts.com/collections/geodes/products/amethyst-geode-cathedral-calcite-19-25-nt-10y

https://cosmiccuts.com/collections/geodes/products/amethyst-geode-cathedral-9-75-ct-49r

We know that is an issue for duplicate content, so I was thinking that setting up canonical tags for them would be the best solution, but I don't understand how to do that because it's very different than just setting up the normal canonical tag that is set up on all websites. 

So my question is 1) are canonical tags the best way to handle this, and 2) if so, what are the step-by-step directions to add it to each product page?

Thank you in advance for any help you can provide!