Navajo Heishi style turquoise black pen shell silver tone two strand necklace

This is an exquisite Navajo Heshi / Heishi style turquoise and black pen shell silver tone metal two strand necklace. It measures 26 inches end to end. The clasp is made of silver tone metal. It probably is sterling silver but since it’s not stamped 925, I’m selling it as silver tone metal. In excellent vintage condition.