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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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Jan 16, 2010 - 02:37pm PT
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Minerals: my guess is that the black mineral is hornblende
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Minerals
Social climber
The Deli
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Jan 16, 2010 - 02:54pm PT
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Close, Tradster.
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Jaybro
Social climber
Wolf City, Wyoming
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Jan 16, 2010 - 02:58pm PT
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Texas Canyon? There are unnamed towers there.
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Minerals
Social climber
The Deli
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Jan 16, 2010 - 03:41pm PT
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Here’s some hornblende in Half Dome granodiorite from Tuolumne. Notice the 60° and 120° amphibole cleavage angles seen in cross-section of the mineral. Hornblende usually appears as black rectangles. Notice the white dots (feldspar) within the hornblende – when a mineral contains smaller crystals of another mineral, the texture is said to be poikilitic. One could describe this as “poikilitic hornblende.” The black minerals that are commonly seen in granitic rocks are hornblende and biotite. Biotite is the soft, platy, hexagonal mineral – it’s a mica.
Hornblende and hybridized mafic enclaves
Amphibole cleavage in hornblende
Hornblende:
http://en.wikipedia.org/wiki/Hornblende
Biotite:
http://en.wikipedia.org/wiki/Biotite
Poikilitic texture:
http://en.wikipedia.org/wiki/Poikilitic
Here are a few from a boulder on the shore of Bear River Reservoir, Sierra Nevada:
No shortage of hornblende in this boulder…
Lots of hornblende and small mafic enclaves
Closer view, showing poikilitic texture in hornblende
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crunch
Social climber
CO
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Jan 16, 2010 - 04:06pm PT
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Tuolumne Tradster's aerial photo a few posts back is of Canyon de Chelly. The big tower is Spider Rock, 800 feet high. The chunky butte just right is Arachnid Mesa, a Todd Gordon FA. You can see part of the road leading to the overlook. That's a lot of snow. Brrrr.
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Fritz
Trad climber
Hagerman, ID
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Jan 16, 2010 - 04:34pm PT
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Minerals:
You (of course) are correct on the first two photos of my quiz.
Epidote & garnet.
Chrysocolla over garnet.
On the 3rd photo of the Mystery Metallic Mineral (3M), I am not sure about the chlorite, and the white is quartz not calcite.
I will post another photo of a more oxidized piece of the 3M.
The mine is on a "tactite deposit, formed by the alternation of limestone blocks by mineralizing solutions from a quart diorite stock".
Specific metallic minerals listed for this mine are: cuprite, chalcocite, covellite, bornite, chalcopyrite.
The 3M does not match up to the dark mineral in your first photo. The 3M seems to be in thin layers or books at this site.
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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Jan 16, 2010 - 04:52pm PT
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crunch: thanks for the canyon id. One of these days I'll have to check out Canyon de Chelly from the ground.
Minerals: your mystery black mineral is in a metamorphic rock...correct? I guessed hornblende because I've seen amphiboles in metamorphic rocks that have that crystal form.
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Minerals
Social climber
The Deli
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Jan 16, 2010 - 05:13pm PT
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Ahh, OK, Fritz. I was having a hard time seeing your original photo – the darker patches that I thought were chlorite are shadows on the epidote. Quartz on the left? Is the shiny stuff in the lower right the 3M or a reflection off a cleavage surface on a non-metallic mineral? I will have to give your second 3M photo some thought. Sure doesn’t look like chalcopyrite or bornite (“peacock ore”). Must be a copper mine.
Well, if the 3M doesn’t match up to my metallic mineral photo above, then we might as well turn it into another quiz! What is it? And what is the main surrounding mineral?
Tradster, yes, the above photo of the mystery black mineral is of a metamorphic rock and the photo on the previous page is of a skarn. This black mineral is a relatively common accessory mineral in pegmatites.
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Minerals
Social climber
The Deli
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Jan 16, 2010 - 05:28pm PT
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OK, Fritz. My guess for the 3M is covellite (CuS) based on your “thin layers or books” description. Had to look it up in my mineralogy text.
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Klimmer
Mountain climber
San Diego
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Jan 16, 2010 - 05:32pm PT
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OK, here is an easy question but an important one.
Q: What geomorphic feature type dominates on all planetary bodies in the Solar System? (Planetary bodies includes planetesimals, protoplanets, dwarf planets, moons, planets (at least this feature dominates on the Terrestrial Planets, not so on the Gas Giant Planets).
The late great Astrogeologist Gene Shoemaker would be proud if you all could get this right, since he really woke us up to this reality.
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Minerals
Social climber
The Deli
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Jan 16, 2010 - 05:37pm PT
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I’ll keep my guess to myself…
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Fritz
Trad climber
Hagerman, ID
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Jan 16, 2010 - 06:19pm PT
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Well Minerals: It's a deep subject. I worked it down to Covellite, but this 3M stuff was hard, and not at all flexible, no perfect cleavage either. Then I thought Chalcocite. It still didn't fit well.
After your answer, something clicked. When I broke open the epidote, garnet,3M specimens: a red powder trickled out. When I thought about it, hematite was the red powder. In my two Geology field reports Hematite is mentioned as common in the district, but not mentioned at this mine. In desperation I tried the streak test on my sidewalk. The streak was red = hematite. I then referred back to "Idaho Minerals" and of course it mentions Hematite in this form at this location.
Hematite = 3M = Mystery Metalic Mineral! I'm sticking to it. Gotta rest now--whew!
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Minerals
Social climber
The Deli
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Jan 16, 2010 - 06:38pm PT
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Hmmm. If you say hematite, then my original guess was right. The photo that I posted is of specular hematite – some of it is metallic and some is more weathered, and darker colored. The streak test will usually do it, though. I thought the brownish color in your second photo didn’t quite fit covellite.
Hematite:
http://en.wikipedia.org/wiki/Hematite
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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Jan 16, 2010 - 09:06pm PT
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Klimmer: in response to your question about rocky planet geomorphology, there's a hint in one of my posts further back in this thread.
Minerals: ilmenite?
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Fritz
Trad climber
Hagerman, ID
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Jan 16, 2010 - 10:09pm PT
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OK! After Minerals worked on my difficult mineral ID: I am going to throw up an easy one.
This specimen is from a "iron-rich skarn" in central Idaho.
Photo shows typical crystals of this common mineral.
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Minerals
Social climber
The Deli
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Jan 16, 2010 - 10:25pm PT
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Ilmenite is found in pegmatites but the jet-black mineral is a little more common than ilmenite. It often has striated surfaces…
Fritz, nice photo – octahedral crystals… I think Klimmer got it.
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Reilly
Mountain climber
Monrovia, CA
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Jan 16, 2010 - 10:27pm PT
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Amphibole cleavage in hornblende
As a geology lurker I love it when y'all talk dirty!
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Fritz
Trad climber
Hagerman, ID
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Jan 16, 2010 - 10:36pm PT
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Klimmer is the winner! A big round of "boooyahs" to Klimmer.
Seriously: the hints were good, but the crystals were not that easy.
Nice job Klimmer.
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Klimmer
Mountain climber
San Diego
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Jan 16, 2010 - 10:44pm PT
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I know my question was easy. You all know it of course . . .
Impact Craters
http://en.wikipedia.org/wiki/Impact_crater
Gene Shoemaker is the man. With the discovery of Comet Shoemaker-Levy 9 and then watching all 20 or so fragements slam into Jupiter, we realized that this indeed can happen in our time. If it can happen to another planet in our lifetime, then it can also happen to Earth. If just one of those fragments of SL9 hit Earth it would have been game over. Just one of those impacts was half the size of Earth or larger. The hunt for NEOs began in ernest.
A great NGS DVD to watch is "Asteroid - Deadly Impact." Goes into this whole story in detail. My students really enjoy it when we study the Asteroid Belt and the differences between Comets (from the Kyper Belt), Asteroids, Meteoriods, Meteors, and Meteorites. Very cool film. I can watch it time and time again. In fact, I do every year with my students. This movie never gets old. Riveting.
National Geographic Video - Asteroids - Deadly Impact (1997)
Starring: Carolyn Shoemaker, Eugene Shoemaker Director: Eitan Weinreich
http://www.amazon.com/gp/product/B00009B8F9?ie=UTF8&tag=ovgcom08-20&linkCode=as2&camp=1789&creative=9325&creativeASIN=B00009B8F9
By the way, there is no other natural disaster that compares to the possible destruction of an Impact. There is a line in the movie where Gene says this and then uses the analogy of all the nuclear armaments on Earth going off at once, and then it would still pale in comparison. Case in point . . .
Asteroid Impact (HD) (music by Pink Floyd):
http://www.youtube.com/watch?v=-zvCUmeoHpw
Nothing like it.
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