Naked Science Forum

Non Life Sciences => Geology, Palaeontology & Archaeology => Topic started by: rswearer on 10/04/2011 01:49:11

Title: What is this rock that's peppered with holes?
Post by: rswearer on 10/04/2011 01:49:11

Greetings everyone. I found this strange rock at an old industrial site in Philadelphia. I know that over the past 200 years there was iron making and glass making on the site. I found lots of slag, but this rock looks different than the rest of the group I collected.

Any ideas? Thanks so much for taking a look!

Title: Re: What is this rock that's peppered with holes?
Post by: Bass on 10/04/2011 05:24:55

Welcome to the forum!

This specimen is oxidized vein rock.  There are several quartz veins with iron oxide staining.  In places the rock is fragmented (brecciated).  The holes are oxidized minerals that have weathered out (or possibly clay minerals from argillic alteration).  Probably some of the ore that was being processed.

Title: Re: What is this rock that's peppered with holes?
Post by: JimBob on 10/04/2011 19:07:59

On the other hand - it could be part of a fossil bone.

What does 10% hydrochloric aid or STRONG vinegar do to it if you put a drop or two on it?

Title: Re: What is this rock that's peppered with holes?
Post by: rswearer on 11/04/2011 22:19:25

Thanks so much for the help. I tend to think that the vein rock explanation might fit better. The rock does, however, look like it has bubbles impressions all over it, though some of this could be due to erosive pitting. If I get some time in the next few days I will post some close-up images of the unusual features.

I will try to acid test too.

Again, thank you!

Title: What is this rock that's peppered with holes?
Post by: rswearer on 12/04/2011 01:55:00

Here are some close-ups of the mystery rock-thing. The feedback is really helpful. Thanks.

Title: What is this rock that's peppered with holes?
Post by: rswearer on 12/04/2011 01:58:38

A few more...

Title: What is this rock that's peppered with holes?
Post by: Bass on 12/04/2011 15:38:23

I stick by my original answer (especially if you can't scratch the white material with a pocket-knife).  There are multiple generations of quartz veins (I'll illustrate on your photos when I have time).  The pits are oxidized sulfides or rock fragments.  Great photos!

Title: What is this rock that's peppered with holes?
Post by: rswearer on 12/04/2011 22:37:54

Thanks once again for your feedback. I will do the "scratch test" when I get home from work and let you know what happens. The rock is really interesting--unlike any other I found at the site. If you get time I would like to see the illustrations on my photos.

(Later) Did the scratch test and found that the white part did not scratch.

Title: What is this rock that's peppered with holes?
Post by: Bass on 23/04/2011 00:54:06

There are at least 2 generations of veining and mineralization.  Red lines show first generation of quartz veining which is cut by the blue (second generation) of quartz, fracturing and sulfides.  The sulfide minerals have since oxidized, leaving the voids.

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Title: What is this rock that's peppered with holes?
Post by: Bass on 23/04/2011 01:06:52

note that the voids, some with oxide minerals, occur at the margins of veins.  Typical of open-space filling veins.

blue= veins
red= oxidized voids
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Title: What is this rock that's peppered with holes?
Post by: JimBob on 23/04/2011 20:22:00

Yep, and in the bottom-most picture in this post - the thumbnail, you can see the face of George Washington at the top, too. 

You are just too good at what you do, Bass.