This is a cabochon of Petrified Wood (or probably agatized wood). What a colorful pendant! The flash across the middle of the cab makes a striking contrast with the peaceful background. If you remember the comic strip character Nancy, you can appreciate the style of the 14K Gold Filled topper (and you're MY age!). I found some of this same material at Quartzsite and the vendor said it came from Texas.

The pendant is 2" high and 1-1/8" wide.