[Boone (OP)]

I recently found this rock hiding away. I found it years ago in a creek bed. I have always wondered what type of rocks they were and how they got formed together. Here are the pictures. It is fairly heavy and appears to have crystal also. I would love to find out what I have. Thanks. Dan

[JimBob]

This is just a guess but it could be layered lava. It depends on where you live. If there are volcanoes around now or in the past,  it could be.

[Geezer]

If there are volcanoes around now or in the past

Such incredible insight! OK JB - tell us one place where there were no volcanoes in the past (he's failing a bit, so we should probably cut him some slack.)

[Boone (OP)]

It is from a timber in Eastern Iowa.

[JimBob]

OK JB - tell us one place where there were no volcanoes in the past (he's failing a bit, so we should probably cut him some slack.)

Western Kansas

[JimBob]

Boone

Can you get a close-up? Also, can you scratch it with a knife or will it scratch glass?

[Boone (OP)]

I'll try and take a better close up, but I might be at the limitation of my camera. I have a much better camera just not with me at the moment. It does scratch glass quite well and I can scrape fine particles off with a knife.



I will try and get some better detail pics during the next week, as I have some other rocks to take pictures of to show off.

[Geezer]

I dunno fer sure, but that looks a mite like that there yellar paint them puts along the sides of the roads in town. Dunno why them does that. Guess them has too much o'that yellar paint.

[Boone (OP)]

I can guarantee it is not yellow paint. This was found no where near a highway. 

[JimBob]

Boone - don't pay attention to Geezer - dementia, you know.

The black layer was there first. It "looks" volcanic. The yellow layer has little parts of the black layer in it so it had to be  the second. I suspect volcanic because there is "rust" in the rock - the reddish stuff.

We need Bass to look at this. If it is igneous in origin, he will be able to tell at a glance.

There is a possibility that it could be ejecta from the Cretaceous impact event in central north west Iowa.

[Bass]

Welocme to the forum Boone!  (Could this be the famous Daniel Boone? [])

The dark part of this rock appears to be igneous- probably basalt or gabbro (igneous rocks low in Si, which are commonly black).  There are obvious crystals oriented in random directions- no foliation- mica layering- is visible (so probably not metamorphic).  Are the crystals in the black layer biotite (black mica)?

As to the light layer- I can't really tell from these photos. Possibly quartzite or granite? There appears to be a thin contact zone in the lighter layer along the contact with the dark rock.  This may be a chilled margin- suggesting the darker rock is intrusive (cooled underground) rather than extrusive (lava).

Boone- can you post some better photos once you get your other camera?  Would like to see more detail of the whole rock, but especially the lighter colored layer and the contact zone.

Given that there is very little to no outcropping Precambrian igneous rock in Iowa (with the exception of scattered granite fragments around the Manson Impact Structure in west central Iowa), I would be willing to give long odds that this is a glacial erratic from Canada-Minnesota.

[Boone (OP)]

I will get some better pictures on wed. As far as I can tell the crystals on the dark part are black, but my eye's could be deceiving me. This rock stuck out like sore thumb among all the other rocks in the vicinity from what I recall. Thanks for the info so far. Boone

[Geezer]

this is a glacial erratic

Sounds more like a description of JimBob.

(Sorry for disrupting your Topic Boone - BTW, Welcome to TNS (The Nutty Scientists))

[JimBob]

My deepest apologies, Boone. Our policy of letting people from the old folks home join and contribute often leads to the behaviors we have just seen in the last post by Geezer. I would suggest you ignore this as we do try to tolerate the more elderly, less stable individuals on this forum even though they can, at times, be disruptive, as just occured above.

Just think of Geezer as you demented uncle who gets tipsy at Thanksgiving dinner and scares the little children by taking out his teeth. While we can't approve totally of the behavior, we remember the good times past and forgive him as he is not really in control of his life any more.

We still love him.

The Geezer =
                   

[Geezer]

Ooooh! Nice graphic. Wonder if I can put it into my signature.

[Boone (OP)]

Here are the best pictures I can get.

[Boone (OP)]

Also a few pics of the other rocks I wanted to show off. The black rock I don't know much about.

[JimBob]

The ones at the top are obviously several deep fried shrimp clumped together.

OR


Hydrothermal or other vados water activity produced these. They are crystals deposited on and in the host rocks - shale or black limestone in the last three picture.

Are there caves in the area?

ALSO if you are in north-eastern part of the state it very well could be shed from the west, the gray area on the map below. This is an area of very old rocks that have been uplifted. They are 1.1 billion years old and were once much wider at the surface. So if they were broken off during erosion it is not far fetched that they didn't move very far.

This is really a bit far fetched.

BUT It Could Happen!

[Boone (OP)]

The first rock location was found in Cedar County IA, east central Iowa. The black shale rock is also from this area. The petrified wood/quartz I do not know where that came from. My father has had them for many years.

[JimBob]

Not Boone County??

BUT, while looking for the Cedar County on a map my eye was caught by the city of Galena, Illinois. Galena is not that far from Wyoming. Wyoming, Cedar County, Iowa, that is. Amazing what you can find on a map! Nevada is also there as well.

As near as I can tell from the geologic map of the US there are mostly sedimentary rocks in Cedar County. (The Iowa Geologic Survey is too cheap to put a geologic map on its site.) BUT, the occurrence of galena, a crystalline mineral, is evidence of intense mineralization in the area of eastern Iowa.  

So there is magma under them there plains.