Vintage 1970s "mexican onyx" stone necklace!

I'm not entirely sure what stone this is exactly. I want to say it's an agate of some sort. I have heard it called "mexican onyx" before, but honestly I still feel like this is an agate. 22" long with a hook clasp. The pendant itself is 2.5" x 2" and has a gold tone around the edges of the pendant. Please inspect and enlarge the pictures to assess the condition of the item for yourself. Please ask any questions you might have. New/Vintage/Pre-owned/antique items are being sold as is. Pictures are not altered and colors have not been adjusted. Due to technical reasons, colors may appear differently on your electronic devices. Pictures may also be enlarged to show better detail. 💎gemstone, 14k, 10k, 18k, sterling, silver, gold, estate, ring, pendant, earrings, loose, natural, stone, genuine, synthetic, lab, diamond, moissanite, vintage, real, gemstone jewelry, engagement, anniversary, promise, wedding, plated, gem, necklace, brooch, fire, crystal, jewel, gift, authentic, collectable, affordable, tested, luxury, natural, opal, emerald, aquamarine, topaz, sapphire, tourmaline, zircon, spinel, investment, ruby, alexandrite, stamped, gift, birthstone, mom, mother, fiance, wife, girlfriend, designer, southwestern, western, native 💎