Mineral Mondays #73 - Barstow Banana Agate

While out in the desert this past weekend I decided to do some prospecting away from the various localities I was collecting at.

Early on Sunday morning I came across a jasper-agate outcrop, actually the whole hill was jasper-agate, but there was a small portion about 3 feet in diameter that was different than the rest. It was an outcrop of a banana yellow agate. The color was really vivid against the backdrop of the reds & browns of the surrounding jasper and desert varnished rocks.

I collected a few pounds of it then continued on to see what else the hill had to offer. Mostly it was reds & whites with occasional wollastonite vugs. I picked up a few pounds of that material too and headed out to my next spot to hunt for barite and after that lazulite at a locality I had to find by rough directions.

It was't until I got home that I really realized what I had found in that banana yellow agate. The patterns and color were amazing and I am kicking myself for not digging down and collecting more.

The agate is what is called a 'plume agate" due to the plume like patterns it creates in a clear agate.

Several pieces had small quartz vugs.

This one had druzy balls of yellow quartz.

But the best specimens I found, only two of them, had purple mixed in.

I did some looking into what could be causing these colors. Yellow is not a very common color in minerals so it's easier to narrow down what causes the color. For example uranium is a yellow mineral. However if this was uranium I probably wouldn't be writing this and instead would have joined Darwin club 6 feet underground. Orpiment, an arsenic sulfide, is also a yellow mineral found about 20 miles away from this locality. Orpiment almost always has orange/red mixed in though so I continued my research.

Most likely what is causing both the yellow and the purple is iron. Ferric iron for yellow color and irradiated trivalent iron for the purple color just like amethyst.

In my research I couldn't find any information on this agate or it's locality so I am naming it Barstow Banana Agate for it's locality and bright yellow color.

It was a great weekend collecting rare gems and minerals and discovering some new localities. That and some classic Van Halen really set the mood for this week.

Thanks for reading!

All photos taken with my iPhone X.

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