Naked Science Forum

Non Life Sciences => Geology, Palaeontology & Archaeology => Topic started by: bluebott on 11/06/2010 04:18:42

Title: Can anyone identify this rock?
Post by: bluebott on 11/06/2010 04:18:42

I found this rock in Fredericksburg, Va.  It was along the side of a street in a new subdivision and looks like it may have been fill material brought in from somewhere else to line the roads as gravel.  Any ideas what it may be?  thanks!

Title: Re: Can anyone identify this rock?
Post by: JimBob on 11/06/2010 16:55:33

Epidote or olivine - As olivine is more likely found in volcanic provinces, I'll go with epidote.

Title: Re: Can anyone identify this rock?
Post by: bluebott on 12/06/2010 23:15:03

Thank you for your response!  I've added two more pictures, maybe that will help?  The first is another angle of this same rock.  The second is another rock that I believe is of the same material that includes the exterior.  Any thoughts?  I really appreciate your help and love reading the boards.  Thank you so much!  Leslie

Title: Can anyone identify this rock?
Post by: Bass on 16/06/2010 02:09:42

I don't think it's epidote or olivine.  epidote doesn't tend to form translucent crystals like these, and olivine never forms in geodes.  More likely is green flourite or calcite. 
A bit more information, like hardness, cleavage and a closer photo would be helpful.

Title: Can anyone identify this rock?
Post by: JimBob on 16/06/2010 02:19:12

We bow to your knowledge, oh great one.

Title: Can anyone identify this rock?
Post by: bluebott on 16/06/2010 04:36:04

Thanks again for your responses!  I'm not sure how to perform hardness and cleavage tests.  To me this feels and looks lot like quartz crystal.  Both pieces are about the size of a walnut.  I tried to post pics from different angles than the previous ones and closer up.  Hope that helps?  Thanks for your time. 

Title: Can anyone identify this rock?
Post by: JimBob on 16/06/2010 18:00:08

There is such a thing as green quartz.

Title: Can anyone identify this rock?
Post by: bluebott on 17/06/2010 02:58:00

Hmmm....I'm leaning toward that or green calcite.  You experts ROCK! (pardon the bad pun)

Title: Can anyone identify this rock?
Post by: JimBob on 17/06/2010 03:52:46

It is OK - I like pastry, too.

Have you noticed our little bun section?

http://www.thenakedscientists.com/forum/index.php?topic=31700.75

Title: Can anyone identify this rock?
Post by: Bass on 17/06/2010 05:08:48

hardness- try scratching the green mineral with the point of a pocket knife.   Cleavage- are there discrete planes (shiny surfaces) when you rotate the crystals against a light?  Does the mineral break in preferred directions?

Both fluorite and calcite have good cleavage, quartz has no cleavage.  You will be able to scratch both fluorite and calcite with a knife, but not quartz.  Let us know the results.

Title: Can anyone identify this rock?
Post by: frethack on 18/06/2010 00:35:08

Wanted to add something.  I noticed this from a closeup of the first pictures of the sample.  It may aid in identification.

At least one of the crystals seems to have a hexagonal form:
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fi481.photobucket.com%2Falbums%2Frr176%2Ffrethack%2Fgreenmineral.jpg&hash=89da131087c76f346821437dfc226d60)

Title: Can anyone identify this rock?
Post by: JimBob on 18/06/2010 02:18:56

Yes, but the crystal just above with the circle part way through it has probable twinning in it, suggestive of epidote twinning.

Title: Can anyone identify this rock?
Post by: bluebott on 23/06/2010 18:59:48

Hello again!  Sorry for the delay in responding.  I was able to scratch this rock and material came off of it.  Also, as far as cleavage, it doesn't appear to break in straight lines.  But does have distinct crystal shapes left whole at the break.  I'm still not sure how cleavage works.  The weird thing is that the crystals all appear to have a rounded shape to them rather than straight.  I'm thinking green calcite?  Thanks for the imput, you guys are great!