Mexican Cantera Opal high quality Pendant Set in Sterling

I have had this beautiful many colors opal for over 20 years. I purchased it in Mexico. It is called Cantera Opal and found in Rhyolite matrix near Queretaro Mexico. Measurement is approx 12 x 10 mm. It is set in a sterling silver mounting meant for irregular shaped stones. Sterling jump ring is attached. I will include a FREE 18" satin cord necklace with sterling closure. high quality