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Geology/Can you help me solve my mystery?

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Question
My rock
My rock  

side of rock
side of rock  
Hello Mr Patton,
My name is Ellen Beaumont. I have had this rock for 62 years. My father found it when I was 5.  It has always been a mystery to our family. Do you have any idea what it might be?
Even though it looks like it has a layer of metal in it, It does not react to a magnet. It weights 5 lbs and is 6 3/4 x 5 inches.  Isn't it "magnificent"   Help...please!

Answer
Ellen:

Her is a link to petroglyph images.  Yours is small but you can see the similarity to some of the angular geometric ones to yours.

http://www.bing.com/images/search?q=small+petroglyph+stones&qs=n&form=QBIR&pq=sm

What you have to my eye is a real treasure.  The outside markings are petroglyphs. Carvings by some stone age indian tribe or neolithic people.

The patterns on the outside cannot to my eye be natural.  Nature usually can make surface lines, striations we call them, for instance the lines left by the passage of ice during glaciation.  Tool marks they are called caused by embedded rocks in the ice grinding against the rocks over which the ice passes.  This cannot be the case of your rock, since there are intersecting lines and curved lines all on the same surface.  These lines have no relationship to the interior stucture of the rock so must have been put there by something etching the surface.  The mix of straight, curved and intersecting lines tells me it was the huan hand.

The rock material is sedimentary.  The lithology of the rock looks to be a very fine sand stone or silt stone.  I cannot tell the cementation but since it is tan to red, I would say quartz silicate stained iron oxide.

Rocks of this type are formed when sediment is laid down by water.  Over the eons they are buried deeper and deeper until a few things happen to lithify them form loose sediment to a solid rock.  Minerals can be carried into the pores by ground water and percipitated cementing the grains together.  Several types of cement result from this, iron oxide, calcium carbonate and quartz cement.  Also pressure and heat can mash the grains together with such force that the start to dissolve into one another, called crystal solution.  This makes a nonpourous almost glass like rock such as quartzite, the round hard rocks in streams you see.  

The interior banding of the rock is a result of one of these processes, the former I would say.

The original porosity of the rock allowed it to be cemented, probably by quartz.  If it was calcite it will fizz when a weak acid is applied to the inner surface.    This happens when the rock is exposed to waters carrying dissolved quartz and it infiltrates into the rock slowly replacing the rock with quartz.  The red and gray are usually indicative of iron and manganese that have been deposited on the surface or sometimes the interior.  This is what you believe is metal.

The choncoidal fractured surface of the broken surface tells me it is most likely silica cement holding the grains together since sandstone or siltstone cemented in other ways tends to break leaving a smoother surface.  This one has no preferred planes of weakness indicating a harder denser cement like silica or quartz.

The interior banding tells me that it was more porous in the past than present.

More than likely the rock is from a desert climate.  The petroglyphs would tell me that it is something from the American Southwest or maybe Mexico or even South America, perhaps the Peruvian Aticama desert area.  I am reaching here, but mentioning areas of known archeological significance.  Did your father travel much?  Could he have brought it back from a trip to those areas?  You don't say where you live but if he found it near your home I would say the Southwest.

In any event, if you live by a university that has an archeology department you might want to contact them for additional help on the surface markings.

It is hard to tell, but the layering the stepped layers on the broken edge is most likely from the mineral layering causing a spalling effect at the broken edge.  I'm not at all certain of this,but it cold be that the outer layer is a clay that was later baked on, but that could be proven if the outer layer is softer than the interior and less granular.  I cannot tell from the photos.  I say this simply due to the number of markings.  Engraving the markings on a hard piece of quartz cemented stone is no mean feat.  The indians of the Southwest did this a lot.  They would scratch through the desert varnish (the thin layer of iron and magnesium oxide to expose the lighter stone beneath making white or lighter colored markings or pictographs in the darker surface coloring.  This is what causes the markes to stand out in greater contrast.  They did this a lot in the Chaco Canyon cliff dwellings in New Mexico.  The rock could have religous significance and may have been used as a marker or totem of some sort.
You don't go to the time and effort of carving something if it does not mean something of significance.

If you do take it to a university be circumspect about where it came from or where you suspect it came from as you don't want it reported that you have a looted archeological treasure.  Even it if was collected by your father 40 plus years ago.  Today the US gov has gotten all knee jerk due to the online cottage industry of buying and selling fossils and artifacts from public parks and lands.  They recently passed laws that prohibit collecting even fossil shells from US gov public lands.  Kids can no longer even collect fossil sharks teeth from the beaches of public parks.  So just ask for some help on what the markings might be and what culture it could be from, and significance the rock might have been.  The indians used stones for heatig water in non metallic vessels, calendar markings, some tribes had stones for weighing down the sides of their tepees.  I don't think it is the latter since that was on the plains.

I hope this helps out.  I would be interested in knowing what you might find out.

You might also try posting your pic on an archeological website specializing in SW Indian archeology.  

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Keith Patton

Expertise

I can answer questions concerning physical and historical geology, environmental geology/hydrology, environmental consulting, remote sensing/aerial photo interpretation, G&G computer applications, petroleum exploration, drilling, geochemistry, geochemical and microbiological prospecting, 3D reservoir modeling, computer mapping and drilling.I am not a geophysicist.

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I have 24 years experience split between the petroleum and environmental industries. I have served as an expert witness in remote sensing, developmental geologist, exploration geologist, enviromental project manager, and subject matter expert in geology and geophysical software development.

Organizations
American Association of Petroleum Geologists
American Association of Photogrammetrists and Remote Sensing

Education/Credentials
Bachelor and Master of Science
Registered Geologist in State of Texas

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