Rockin the Rockies

Rockin the Rockies
Stowe Mtn

Saturday, August 29, 2015

Orthoclase Crystals Near Mosquito Pass

Top of Mosquito Pass used by stagecoaches long ago
Just west of Mosquito Pass and east of Leadville, Colorado is a fairly well known area for finding twinned orthoclase crystals. I had been to this site many years ago on a club field trip and thought it might make for an interesting diversion to an All Terrain Vehicle (ATV) trip my digging partner had planned. While orthoclase crystals don’t excite me too much, the fact that many of the crystals are penetration twins (Carlsbad) makes them desirable for the mineral collector. http://www.uta.edu/faculty/mattioli/geol_3313/Feldspar_Twinning.pdf 
We drove through Fairplay, CO, parked the vehicle and headed up the east side of the pass on ATVs. The visibility was somewhat restricted due to fires in western Washington, Idaho and Montana, but better than the last few days. There were many things to see including wildlife, abandoned mines and friendly people along the 4-wheel drive road.
Marmot warming up
As we crested the pass my foggy memory cleared of where the exact crystal site was and we motored down the pass quickly reaching the old dig site. I reread some material by Voynick, 1995, Colorado Rockhounding to help refresh my memory of the location. The twinned orthoclase crystals can be found in quartz monzonite porphyry outcrops. Near the digs you can see host rock with the orthoclase crystal indentations in them. The ground was also scattered with what appeared to be pea-size or smaller octahedral quartz crystals that had weathered out of the host rock. We dug into the side of an old dig and found the occasional crystal weathered out of it's host rock. No pockets of crystals here, but time and a little determination yielded results.
Digging area
 We only spent a little over an hour at the site but did find a few collectible crystals. I read that Carlsbad twinned orthoclase crystals up to 2” can be found so after finding one double terminated crystals of 3” I figured I could do no better and it was time to continue our ATV fun. My digging partner generously provided the transportation and made for a very enjoyable day. This particular site is more easily accessed by 4-wheel drive vehicle from Leadville but either way you go to this 12,000Ft dig site be mindful of your 4-wheel abilities, altitude and the changeable weather.
Some dendritic manganese patterns on the crystals