On beautiful Saturday, Nov 10th, 2018 we explored the borate area near Boron and neighboring volcanics. We met at 9:00AM in the Rio Tinto Visitor Center parking lot. We welcomed some friends from Southern California Fluorescent Minerals Society and Southern California Friends of Mineralogy.
At the Visitor Center we watched a short movie about the mine pit history and borax products. There is a giant yellow borax crystal inside a climate controlled box.
In another room there is a mineral exhibition featuring giant kernite block and other minerals from the pit including colemanite crystals and datolite nodule. For more information go to https://www.borax.com/borax-operations/borax-visitor-center
We went up to the viewing terrace above the Visitor Center to see the pit panorama and have a quick overview of the pit geology. The mine is operating on a ancient lake bed where boron minerals concentrated over thousands of years.
Before leaving we admired the 11 feet tall tire and then collected a few crystals of ulexite, probertite, and kernite from the small material piles brought by the mine workers from the pit to the Visitor Center parking lot.
Afterwards we drove over to the Saddleback Mountain for opal, magnesite, and calcite vein material. The opal is very strong green fluorescent under shortwave UV light. Under longwave UV light the vein material fluoresces in 3 different colors: white for magnesite, yellow to orange for calcite, and less intense green for opal. The matrix rock is Saddleback Basalt, supposedly the same layer as the base rock in the Boron mine pit. In the vesicles you can potentially find clear labradorite, augite, and quartz pseudomorphs after tridymite, covered with white montmorillonite. We did not see any tridymite pseudomorphs this time, but everybody found nice opal vein material with calcite and magnesite.
The last leg of the trip was focused on microscopic minerals at the “pumice” quarry 1.5 miles northwest of the Saddleback Mountain. The finds included small but interesting zeolites like heulandite, chabazite and phillipsite, and also interesting aggregates of clear lustrous hexagonal blades of magnesite. Some beautiful analcime crystals and natrolite needles were found in an olive colored basaltic rock. The historical articles also mention micro pseudobrookite and more rare minerals like searlesite and smythite. We found no pseudobrookite this time, but apparently some searlesite and smythite were found in the basaltic rock.
For people more interested in rocks rather than minerals the area offers dark red jasper. We found a lot of it on the desert floor north of the Boron mine pit dumps. A few miles to the west of the pit there are more areas with petrified wood as well, we did not visit them this time.