The Key To My Heart Project

I will be casting my next project. My client wants a 2 inch key with a heart top. I am not sure how to approach the project but I do have a stone that I cut for my x that I didn't have an opportunity to set. It makes me sad to see it, so I may as well use it and get on with life. The stone is Rhodochrosite, a rare stone that I have had in my toolbox for over 20 years.