Before I tell you about my road trip, let me answer the most common question I hear about peridot: is it pronounced per-ə-ˌdät or per-ə-dō(t)?! As my father would say, the answer is “yes”. Both pronunciations are correct.
I recently took a road trip to the town of Peridot, Arizona (locally pronounced per-ə-ˌdät). Peridot Mesa is the premier location for mining the gem in the United States.
The peridot mine is located on the San Carlos Apache Indian Reservation. Collecting in this area is very strictly regulated; you must obtain a permit and even then you can only access the area when guided by a claim holder. Once at the mine, you must remain on the claim owned by your guide. I was able to visit the mine with Stevie Joey, who has been mining his family’s claim for many years. Most of the work is done using a jack hammer, but larger equipment is brought in to move overburden material and open new locations.
The peridot crystals are found in peridotite xenoliths (say that 10 times fast). Xenoliths are pieces of preexisting rock that are ripped out of place as molten magma moves through the depths of the earth. The earth’s upper mantle consists of peridotite, a rock composed of olivine as well as several other minerals. The magma picked up pieces of peridotite and carried them to the surface. The heat of the magma started to melt the rocks resulting in the rounded edges of the inclusions (see photo below left). Olivine is the green mineral in peridotite and when it’s found in gem quality (good color and clarity), it is known as the gem peridot. The peridotite at the mine is very crumbly which is why there’s so much green sand around. The rock surrounding the peridotite xenoliths is basalt – the rock that forms when lava cools. So what we’re seeing here was part of the earth’s mantle – pretty darn amazing!
Most of the pieces of peridot I found were very small, but larger pieces can be found. I tried to remove the large dark crystal in the photo above right, but it was internally fractured and didn’t make it out in one piece. I came home with a few nice samples of peridotite, but no large pieces of peridot. An opportunity to see one of the world’s most interesting source of gems was an adventure worth having!
References & Resources:
Peridot and peridotite:
Photos (c) 2018, J. Fenton