How to tell the age and type of a rock?

Question

Is it possible to tell the age and the type of rock a rock is by simply looking at it?

For example...

take this rock

http://i240.photobucket.com/albums/ff305/tjpetrowski/100_3075.jpg

What type is it (i.e. Metamorphic, Igneous, Sedimentary - even better as to the actual rock like limestone or something). How did you identify that?

How old is it and how do you know that?

What about these rocks...

http://i240.photobucket.com/albums/ff305/tjpetrowski/100_3080.jpg

http://i240.photobucket.com/albums/ff305/tjpetrowski/100_3084.jpg

No, this is not for homework. Simply interest.

Answer 1

<<Is it possible to tell the age and the type of rock a rock is by simply looking at it?>>

Generally, no.  With experience, some types of rock from particular places are very distinctive to people used to closely looking at them.  One case is rock from Solnhofen in Germany.  Show the quarryman (or acquainted geologist) six specimens of limestone from different places which look vaguely alike, and they'd probably identify the Solnhofen one with no problem.  In those sort of circumstances, they could then tell you the age as well.

Answer 2

Basic geology for you...

Sedimentary is rock laid down from other [rocky] material such as silt which is then compressed by the layers above it.

Metamorphic is rock such as sedimentary that has then been buried and subjected to heat and/or pressure and becomes a new type of stone.

Igneous is rock that is extruded in one form or the other from the earth's mantle as lava and then solidifies.

Photo one and three look like granite and so is Igneous and coarse grained.

Photo two is a little unclear, could be metamorphic fine mud stone [or similar] that has been morphed to slate or schist or actual sedimentary rock itself or could even be a fine grained basalt that has been river worn.

Aging rock is never easy, there are known events that appear as traces in sedimentary rock, radioactive dating is used. Because certain elements decay, and do so at a constant rate, and decay into daughter elements one can compare the ratio of mother to daughter elements and work out how much decay has taken place and ergo how much time has passed...

And of course, we know (for any given value of know) when certain creatures exisited, or can work out when a new inter period species is discovered and this can determine when the rock was laid down, which works for sedimentary but is a little harder for marble! Go Figure.

the rocks i personally enjoy is Flint with its chalky casing. Worth looking into and then you will never walk past a gravel drive again, most exciting in this area is flintstone with imprints of sea shells and rarely actual shell itself which has undergone mineral replacement. Sorry, I'm starting to sound like a geological geek!!!

I use wiki a lot and there are good sites out there to look into further...

Answer 3

I'm not sure if you could do that at your own house... but in science class we learned scientists date fossils and rocks by using radioactive dating and stuff like that. I'm not quite sure how it works, but you could probably just type "radioactive dating" in google search and you'd find something. Hope I helped somehow.