Tuesday, November 27, 2012

rock ID

Lockwood will ID rocks/minerals for you on twitter! I mention this as a public service because mineral IDs aren't really my thing. I know, I know. With my lack of interest in mineralogy and my inability to discuss the structural history of a site on demand, I am in danger of losing my "geological expert" badge.

I'm pretty good with the basics (quartz! various micas!) and some of the more distinctive minerals I may come across, such as pyrite. Given a hand sample with reasonably visible mineral grains, I can come up with a good answer. I will admit that I was recently confused by a rock with what looked exactly like dogtooth calcite (an example from here).

It was actually quartz.

That's why I'm not very good at mineral/rock IDs from afar. I need a screwdriver to poke at it and a hand lens to peer at it from different angles. And most important, I need to know the context - what are the conditions it grew under? What are the other minerals it's associated with? I need a big chunk of rock, and maybe a few different chunks to see variations.

My suggestion for identifying minerals and rocks would be to get a field guide with good photos first, and then ask follow-up questions of internet experts. Sometimes doing your own scratching and turning in the light is all you need.


Lockwood said...

Thanks for the shout-out. I agree, trying to get some info first hand, then narrowing it down with a good guide is far preferable- first, it's a powerful learning experience, and second, the finder/questioner is as a rule going to have better info available than a person simply looking at photos and verbal descriptions. However anyways, the web. It makes people lazy, uncertain of their own abilities, eager to defer to "experts," (which I'm not, by any stretch), and impatient. My point was to encourage people to do more than simply snap some quick shots, and to get a little more data that could be very helpful in narrowing possibilities.

And as an aside, I would have first guessed dogtooth spar on that photo, too.

Short Geologist said...

I guess I was unclear - the photo is of dogtooth calcite. I don't have a photo of the actual quartz sample available, but it looked just like the posted photo.