If you caught my post last weekend about Liberty Sculpture Park, you'll know I've been spending a lot of time out in the desert digging for gems and minerals. One of my favorite gems to dig for is opal. Believe it or not California has a lot of opal. This is due to all the volcanic activity in the past 2 - 20 million years. Those eruptions laid down blankets of ash all over the southwest US which allowed opals to grow. Now, we just need to find them and dig them up.
The opals I was hunting are mainly common opal, sometimes called "potch", probably named by some guy who was bitter they weren't precious opal. I never use the term potch because it sounds cheap and these beauties are anything but cheap.
A quick geological lesson. Opals are formed by water infused silica seeping into cracks in rocks. The water eventually dissipates, but some is left behind with the layers of silica spheres and becomes opal. If the layers and impurities are right the silica spheres arrange perfectly to allow light to diffract through them giving the opal "fire".
The trip started out at 9am when I met my rock club on the road to our destination, Scout's Cove.
The black mountain we were going around is an uplift of basalt from older geologic times.
The road up was fairly decent, some sand, some bumps, and some boulders, but overall an easy drive for a pickup truck with high clearance.
After about 40 minutes driving from our meeting spot we made it to the turn off into Scout's Cove, BM7414.
Scout's Cove was originally a precious opal mine from the early 1900's. Precious opal is found here, but the majority of it is about 100 feet down in a very hard host rock. Tiffany's Jewelers was invested in the mine as they were in many gem producing mines through out Southern California. However due to the difficulty of mining the opals and opal discoveries elsewhere the mine was abandoned.
As we arrived 100 years of activity was obvious. Tailings piles littered the cove and surrounding hills.
The miner's hut at Scouts Cove was carved out of solid rhyolite by the early miners.
As I was getting my tools ready I realized my rock hammer was missing. On the way out to meet my club I stopped by another collecting spot and left my hammer out in the middle of the desert. That's why I bought the new sledge hammer in my last post. I had my pick and a secondary hammer though so I got to work.
There are several different kinds of opal up here. They are precious opal, which comes in white, translucent orange(like the photo above), milky orange/peach, black and red. The latter we will get to.
This particular spot has these white, rhyolite outcrops where the translucent orange grows in veins and pockets.
After about 2 hours of collecting we moved up the road a bit to a zone that produces cherry opal(red) and the orange/peach opal.
I immediately got excited about this opal. The orange/peach color was amazing. It looked very much like taffy or ice cream. The red color was intense and small flashes of fire were present in some of the red.
Looks like candy!
The cherry color did not grow in large veins or vugs like the orange/peach did. This is interesting and would probably make for a good geologic paper if anyone wanted to study exactly why.
The matrix of these opals was a hard jasper and appeared to have petrified palm root in it as well. This would make sense as just down the mountain there is a prettified palm root collecting area of almost identical rock.
What baffled all of us was the color. What caused these interesting orange, peach and red opals to form? The orange/peach opal was also found in quantity at our first collecting spot, the white rhyolite, which was totally different than this jasper matrix. As I am not a geologist I can only guess that the silica source had traces of something like iron in it to add coloring. It's a mystery!
As we called it a day and I got home 2 days later I was called back out to Scout's Cove. I just couldn't get my mind off that orange/peach opal and the fact that there is precious opal up there. So, I headed back out the following weekend!
There was a large rock outcrop just before the white rhyolite locality I wanted to look at that we had skipped on the previous trip.
It turned out to be a massive, opal infused blob of jasper, the same material we had found the cherry & orange/peach opal in. This outcrop had white as well, which led me to believe it could have been the original source for the old mine.
The mine has since been filled in by the BLM and no trace of it's location is identifiable.
The nice thing about this opal outcrop is it has been exposed to the elements for millennia. What that means is heating and cooling of the hot desert fractures the rock along the opal seams making it easier to pry the rock apart.
I spent all day on Saturday collecting in the cove at all 3 locations getting enough material to keep me busy for a while.
The area is very remote, but both weekends large groups of off roaders came to check out the cove. We chatted with them and explained what we knew of the history and geology of the area. It appears to be a very popular area for off roaders to visit.
Looking down at the outcrop to the right and the white rhyolite area with the miner's hut in the center of the image.
Living in Japan I've come to realize a large part of the world doesn't have desolate, empty, but beautiful geology like we do in the States. So I'll end with some scenery photos and a few more opal pictures.
Tomorrow I will do a follow up post on how my Hunting and smashing Pegmatites went.
If you want to read about me digging precious opals in California you can find that post here: @rt395/friday-s-rock-california-precious-opals
