Hi, fieldtrip friends!
Let’s get out into the West Mojave desert again for a trip to the Columbus Gem mine a few miles south of Daggett. We will meet on Sat, Apr 23th, 9:00 AM at the south side of the Daggett-Yermo Rd exit off I-40, 7 miles east of Barstow at the following coordinates: 34°51’10.3″N 116°53’27.8″W (34.852846, -116.891062). When coming from Barstow it’s marked as Exit 7 towards Daggett. It is 111 miles, less than two hours of drive from Pasadena. Try to not be late as the mine is not shown on topo maps and it will require some searching around to find the main group. We will continue for about 2 miles south towards the Daggett Ridge on a dirt road. After some initial roughness for a couple of minutes, the road farther up is pleasantly smooth and devoid of rocks. Normal clearance, 2WD cars will enjoy it. Taking a Corvette is not recommended though.
Here is the link to Google Maps directions: https://goo.gl/maps/DwbE5AVEoKn8GpFY9
The weather forecast currently shows a cooling trend for that weekend and another heatwave afterward. It might be the last chance to get out collecting before the heat takes over completely — that’s why this trip is called on such short notice.
The Columbus Gem mine (Mindat location) was famous for great colemanite crystals many decades ago, but it looks like all good borates have been mined out. Today we can find tapered strontianite needles, massive and in vugs, up to 1 cm in size. Strontianite is strontium carbonate and reacts to acids quite strongly. Under LW SW it fluoresces in pale yellow color. Also, in some vugs, you can find celestine, strontium sulfate mineral, as gemmy clear prismatic crystals up to a few mm. Under LW SW it fluoresces bluish-white.
Other minerals of interest are gemmy brown calcite up to a few cm in size (dark yellow fluorescent) and daylight pale green fluorescent hyalite opal. It has very strong green fluorescence under UV light but is quite rare at the site. I observed some tiny bright yellow grains under the glassy layer and it could be a uranium mineral. The UV collectors will be quite happy with the selection this mine offers!
Just behind the green shale, higher up the hill, there is an extensive vein of banded chalcedony. The bands vary in color from light grey to brown and almost black. It will be a great addition to your chalcedony collection. It also looks like great lapidary material. Not even to mention that the lighter bands also have yellow fluorescence.
Less than a quarter-mile to the east there is another small dump with green rocks, but it also has rounded concretions like the ones we saw at the Borate field trip. These, however do not small when broken up. Instead, you find sparkly layers of heulandite covering the fractures.
Hope to see you all there,