Full title: An Instant Guide to Rocks and Minerals: The Most Familiar Rocks and Minerals of North America Described and Illustrated in Full Color
Published January 1st, 1991, ISBN 0681411724, out of print but several used book retailers have paperback copies averaging ~$1.99 USD
Back in the Dark Ages before the wonderful internet became so convenient and the rise of AI tools, I loaded my writing shelves with handy reference books.
My paternal uncle is a geologist who retired from the DNR (Department of Natural Resources). My uncle was looking at some of my descriptions of rocks and minerals (this was when I was only writing fantasy tabletop RPG material on an all manual US Army surplus 1960s Smith Corona Super Sterling - which I still have) in my writing and suggested this book.
Most of this material is available online now, but flipping through the book (and others like it) gave me great visual writing clues for unique treasure with unusual rocks and minerals, such as a gold herringbone necklace with a large teardrop shaped pendant of fossil limestone.