Rockhounding the Rockies: Vug Clay at Lake George

Tuesday, May 14, 2013

Vug Clay at Lake George

Another day rockhounding at Lake George and another pocket of crystals. This is one of the first times I've run into blackish purple greasy clay in a crystal pocket. Most often the clay is either reddish (iron-stained) or yellow. I've also run into grayish material. The particular pocket I was in this day had blackish purple clay and the crystals were not very collectible due to breakage and additional quartz overgrowth. I like clear quartz over smokys which gives the illusion of phantoms or ghost smoky crystals, but not the granular/rough opaque quartz overgrowth on smokys. We sometimes say the smokys are hooded when this happens. I got into a discussion with my digging buddy Bob regarding colors of clay and if that has any correlation to the quality of crystals found in the clay. We both have had very good luck with red clay and poor luck (crystal quality) with blackish purple clay. I'm afraid our sample size is not sufficient to make any conclusions. Anecdotally crystals found in the yellowish clay are harder to clean and the smokys don't seem to have the same lustrous exterior as those found in the red clay. This got me to thinking is the clay in the pocket from the surrounding material or is the clay a result of the soup left in the miarolitic pocket after crystal formation. Since every pocket I've ever found has been broken imploded/exploded I'm guessing it's a mixture of leftover vug material and surrounding decayed/weathered pegmatite. I decided to do a search on the internet and not only was there a discussion about clays in miarolitic cavities but it concentrated on the Pikes Peak Batholith see Mineralogy and Provenance of clays in Miarolitic Cavities of the Pikes Peak Batholith, Colorado. by Kile. While this article was a little above my head scientifically speaking, it seems part of my hypothesis is correct, that the clay is from both the leftover vug material and surrounding weathered pegmatite. The article mentioned the clay varieties smectite, Illite and kaolinite being predominant in the vugs (never knew there was so much to know about clay). The author also mentioned infusion of material from hydrothermal processes after the pockets form. I think some of the fluorites are formed that way. My bigger question was unanswered, does the color of the clay in a pocket have any correlation to the quality of the crystals therein. Does the color of the clay indicate a higher concentration of elements inhibiting crystal formation or luster? Enough investigation for one day. Here are some pictures of the latest dig....