Thursday, March 15, 2007

Geology Pic - Ice Grillz!

So I've decided to just keep posting geology shit, regardless of the day, since its obvious that I can't stick to a Friday schedule with work and such.

This past week I was out doing field work in Crested Butte. One of our tasks was to dig out the entrance to this old mine adit, go in, and service a trough that was in there.

As it turned out, the mine adit was buried under no less than 15 feet of snow - completely blocked.

After tear-assing around on snowmobiles for 2 hours, and then 1 hour of shoveling we finally were able to get into the adit, and saw some really really cool ICE.

There were two main types in the adit: nice crystalline crusts on all of the overhanging adit beams, and large completely clear stalagmites of ice that apparently formed from water dripping from the ceiling of the adit.

There's a classic question in Mineralogy: is water a mineral? according to the classic definition of a mineral, Ice is indeed a mineral, it just has a melting point much lower than the ambient air temperature in many parts of the world.

Water crystallizes in the hexagonal crystal system, which means that while it may look wierd and different and that "no two snowflakes will ever look alike", Ice crystals always have six 2-fold symmetric axes.

If you look close in the below picture (as always, click to enlarge), you'll see a number of ice crystals, and they all have six sides. Its kinda cool because ice doesn't usually form nice big crystals like this, its usually snow, or frozen amorphous ice, or in random cubes slowly cooling down a gin and tonic. To be sure, the temperature of the air in which the ice crystals form has more to do with how the crystals will look than anything. Colder air will form different ice crystals than warmer air will.



Here's another pic:



The same principle is true for alot of minerals. In fact pyrite and other sulfide minerals are often associated with copper, gold and silver. in order for gold and silver mineralization to occur, groundwater has to be at an appropriate temperature and condition. So, if you want to find the gold, look for the pyrite crystals that have the right shape. The shape of crystals is called the habit. The same mineral can occur with many different habits.


EDIT: my good friend sara (without the "h") suggested that these crystals look kinda like Depth Hoar- an ice crystal morphology that I was unfamiliar with. Apparently depth hoar forms by sublimation within snowpack, and can contribute to snow instability in avalanche prone regions.

The crystals above were formed inside of a mine adit, where humidity was higher than ambient air, and the crystals formed on the cross-beams in the adit. Could these crystals have formed in the same way as depth hoar - by the nucleation of water vapor? seems both possible and likely... Thanks for the suggestion Sara!



Another Habit in the mine adit was these wierd looking amorphous clear ice stalagmites:





I'm not exactly sure how these formed, but they were everywhere. My wife told me that they all looked like "just a bunch of dildos". Not sure if thats how my Mineralogy professor in college would have classified them, but I guess the resemblance is close enough.

3 comments:

Karen said...

I'm afraid you misquoted me, Mr. Rock Man. (Bloggers!)

Very cool photos nonetheless.

Sarah said...

Aside from TMI,
the pics are wicked cool.

MOM said...

It looks more like a great adventure than a job, lucky you.