In search of Barite and Topaz

The Granitic Tarryall Mountains, power lines and road signs.

   Some people choose to go to Mexico for spring vacation. Some people choose California, more choose Las Vegas, and more still like to take their break in Moab, Utah. Myself, I like Colorado.

I began my vacation by driving to Tarryall, to look for some Topaz that was rumored to be around these parts. The granitic mountains here are very pretty, and the scar of the massive Hayman fire that ripped through here years ago is beginning to heal. I spent the afternoon hiking the region accessible from Spruce Campground (or something like that), and looking at a lot of granite. Topaz crystals form in granite pegmatites, which are known to be found (in abundance) in the region.

A rundown on pegmatites:

      As a large body of granite is cooling (granite by definition cools very slowly), it is changing from a liquid to a solid. Large crystals are forming as the rock cools, but in a certain sequence of the available minerals. All materials melt at different temperatures, thus they will crystallize and come out of solution in the opposite order. As the rock is cooling, minerals that remain in solution tend to be rare earth minerals, and concentrate along with quartz, which has a very low melting/crystallizing temperature and form pegmatites. Beryl (aquamarine), Tourmaline, and Topaz are all examples of the gemstones that can form from the extremely slow cooling pegmatites. 

A perfect example of a meandering river, with some geese
standing on rocks most likely moved by glaciers

I found one pegmatite that had been excavated. The opening was 20' wide and 30' tall, with very steep sides. Contrasting to the entire mountainside, the walls were made up entirely of quartz. I carefully examined the walls for any sign of pockets where the crystals could form, but didn't see anything. The tailings didn't look too promising either, but I figured if somebody had come all this way to dig out that much rock, they had ought to have a darn good reason. I camped that night by the Colorado Topaz Mine, where an old screener box was sitting, without the screen. It looked like they had been digging around all of the large granite boulder sitting through the camp area. The nearby Colorado Topaz mine  is a  placer deposit of gem-quality Topaz, and has been a very sound producer. In the morning, I dug up a bucket of my own material to screen out when it wasn't freezing. 

The hole in which the barite was found. For scale, the green
screen in the upper part of the picture fits snugly inside the top of
a 5 gallon bucket. It was kinda nice to get out of the wind.

Driving on to the next stop, a barite crystal locality, I soon found myself in someone else's hole. Barite is a heavy mineral used for oil drilling as a thick mud, but occurs in CO in a rare blue variety. They occur in sedimentary rocks, and a formed under low pressure and temperature. They had dug down to the crystals, and must have either had their fill or gotten tired, because they left them exposed in the bottom of the hole. Sure, it wasn't the best hole for proper digging posture, and there wasn't much room to move limbs about, but it gave plenty of license for creativity.  After spending some time cleaning the specimens up, some are quite pretty, and I hope to return soon to dig out some more. The crystals will absorb UV light throughout the day and become more and more blue, so they are very pretty in windowsills.

Here the elaborate crystals are exposed in a mud filled pocket.
The bulk of the mud easily washes away, but the cracks are
filled in with mud, calcite, and iron oxide, but this is all
 easily dissolvable in a strong acid.

In the same day, I drove to Nathrop by Buena Vista, and in the whipping winds and ocasional flurries of snow went searching for garnets and yellow topaz that was rumored to occur there. It was so cold, so I practically ran to the top of the mountain that is of a certain rhyolite that is quite distinguishable. I looked all along the way, but only found one small crystal that I think has a chance of being a topaz because it is squarish and yellow/brown. I found out later that you need to split lots of rocks to find the gems, which I didn't split a single one. Regardless it was beneficial just to look at the geology of the area that they occur in, and now I know just where to go and what to do when I return this summer.

After and exhausting two days (and with a large oncoming storm front) I drove back to Boulder, ready for warmth. When I got there, I sat down, and wished I was still digging in a hole somewhere.

I guess thats just how it is.