MadSci Network: Earth Sciences

Re: What is the difference between a rock and a fossilized bone?

Date: Mon Jul 23 16:58:43 2001
Posted By: David Scarboro, Faculty, Earth Sciences, The Open University
Area of science: Earth Sciences
ID: 994790841.Es

In answer to your question, it is impossible to make a definite judgment 
about your material without seeing it.  If you could send a digital 
photograph of a good example I might be able to identify it.

Two things that I can say, however, are:

(1) It is not uncommon for geological processes such as weathering and 
erosion to fashion rocks into shapes that resemble bones or other organic 
remains.  Most museums are familiar with such items brought in for 
identification.  For example, I have seen the conchoidal fracture on a 
piece of broken flint (resembling a fracture on a piece of a broken glass 
bottle) mistaken for a fossil bird footprint because it happened to 
produce a three-pronged shape.  A fossil collector whom I know once 
misidentified a piece of rolled mudrock which fell out of the centre of a 
suspicious concretion as an ichthyosaur flipper bone!  It did look rather 
like a bone!

(2) The rocks of North Georgia are broadly of two classes, neither of 
which would contain vertebrate fossils.  One type is crystalline 
metamorphic rocks such as schist, which is formed about 30 km deep in the 
Earth’s crust by high pressure and temperature, and could never be host to 
a fossil of any kind.  The other type is sedimentary rocks of marine 
origin from the Palaeozoic Era, such as shales and limestones, which 
contain fossils such as trilobites, but which are too old to contain the 
remains of large vertebrates, and certainly not land-living vertebrates.

Still, there is always a possibility that you have something.  Relatively 
young sediments ranging from a few tens of thousands to, say, a couple of 
million years old, occur as what geologists call superficial deposits on 
the surface in many areas where the underlying geology is much older.  
Such sediments are often poorly consolidated clays and sands, as they have 
not had time to become hard rock.  Here in Berkshire, in England, there is 
a Pleistocene age river gravel quarried for aggregate that sometimes 
yields elephant teeth – I know, because I was present when one of my 
students found one on a field trip to a local quarry!  Such sediments do 
often yield fossil bones of mammals and other vertebrates.  So, if you 
want to email a photograph I’ll be glad to have a look!

Kind regards,

David Scarboro

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