Anyone good with rocks?

[SAR-EMT40]

Can you tell me what this is? I have an idea but am not sure. I would like someone to tell me what it is if they can. I am talking about the mostly black items embedded in the rock.

Thanks,
Keith

 

[Jazzbo]

Need more information

Where is the locality where you saw this? This helps alot.

 

[Fitz]

Kyanite Crystals

That is a metamorphic rock and the crystals appear to be kyanite crystals.

When a sedimentary rock gets exposed to the proper temperature and pressure those crystals form in the new metamorphic rock. Staurolite and mica, garnets, chlorite etc. are also common minerals in metamorphic rock.

 

[SAR-EMT40]

Actually it was on Tuckermans trail just below the first bridge.

Thanks Fitz, anyone else.

Keith

 

[David Metsky]

Those are crystals grown in situ, not inclusions into sedimentary rock. Beyond that I'll defer to Fitz.

 

[bill bowden]

kyanite inclusions?

General explanation: Most of the rocks in the White Mountains are what is referred to as igneous or metamorphic rocks; ones that have been melted or almost melted and then cooled over a long period of time.
Our typical granite (and the various varieties of granite that are called monzonite etc.) include both mica, quartz and feldspar. If this granite is heated almost to melting and cooled terribly slowly the tiny crystals grow much larger and can separate more into discrete crystals. The feldspar can grow into large crystals, some with sodium,others with potassium. The potassium ones are both harder and less susceptible to weathering, so the apparent inclusions are the potassium form. The phenomenon is just uncommon enough to be a little unusual but still fairly easy to find on rocky trails.

 

[adkleaddog]

That is a metamorphic rock and the crystals appear to be kyanite crystals.

When a sedimentary rock gets exposed to the proper temperature and pressure those crystals form in the new metamorphic rock. Staurolite and mica, garnets, chlorite etc. are also common minerals in metamorphic rock.

Good call! They DO appear to be Kyanite crystals....

 

[Fitz]

Littleton Formation

I don't have a geologic map in front of me, but based on the location where it was found, this is probably a piece of the Littleton Formation (composes much of Mt. Washington). It is a metamorphic rock and as Dave mentioned the crystals grow as a sedimentary rock is exposed to higher pressure and temperature - I think kyanite shows up at about 3 or 4 kb and about 500 degrees.

This rock never melted, but was only metamorphosed - mineralogically changed with the heat and pressure.

 

[dr_wu002]

Good call! They DO appear to be Kyanite crystals....

Well, I'm still going to take my X-ray diffractometer next time I hike Tuckerman's.

-Dr. Wu

 

[skiguy]

Well, I'm still going to take my X-ray diffractometer next time I hike Tuckerman's.

-Dr. Wu

What ever you say Lex Luther

 

[Paradox]

Well, I'm still going to take my X-ray diffractometer next time I hike Tuckerman's. -Dr. Wu

Easier to bring the material to the XRD. You don't need much of a sample, a few milligrams at most. ...Now, who do I call?

 

[dr_wu002]

Easier to bring the material to the XRD. You don't need much of a sample, a few milligrams at most. ...Now, who do I call?

Oh, now you're saying that I'm not tough, huh? You think I'm one of those sissies with a little rock-hammer, don't you? I got a pack for This puppy -- it can even do Pole Figures!!

Hell, I'm feeling up to the challenge now -- I might even take my RHEED Gun!

-Dr. Wu

 

[bill bowden]

Wrong machine Doc

Maybe you could pack in one of our Miniflexes just to make sure. I'll get you a manual next time you are in needham.

 

[dr_wu002]

Maybe you could pack in one of our Miniflexes just to make sure. I'll get you a manual next time you are in needham.

Bill, I quit Gillette over a year ago. But -- I'm still good friends with Krasi and Neville. Ask them if you and I can borrow their XRD for the weekend!

We'll figure out that durn rock for sure!

-Dr. Wu

 

[forestgnome]

This was an awesome thread!!! Thanks!

Happy Trails

 

[Jazzbo]

Here is a link to wikipedia picture of kyanite. My Roadside Geology of NH book says Sillimanite found in Presidential Range. Geology sites say Simmanite is found with polymorphs Kyanite and stuarolite in highly metamorphic rocks like in Presidentials. Looks like Fitz is the winner. He wins an Xray Refractometer.

Wikipedia image of kyanite