[Rockhounds] What is this rock?

Thu Nov 13 18:11:59 PST 2008

Well, it's in the fish tank, now, for better or worse.    Doesn't seem to 
have messed up my tank chemistry too badly yet.    I did scrub them well 
with dish washer detergent (stronger than bleach), let them sit outside in 
bleach, then scrubbed with scouring powder, then boiled them.   And all this 
BEFORE I tested them with toilet bowl cleaner.

But are you telling me if I'd washed the rocks in hydrochloric acid they'd 
probably have lost their carbonate?

I know that some parts of the rocks fizzed and others did not but never did 
determine why.  I did notice that worn curved surfaces fizzed more than 
surfaces where the rock had been broken.  My sister got the rocks by going 
out of the house in the rain and picking them up nearby, and I think they 
were originally a single rock or parts of a larger rock.   They look as 
though they may have spent time near the road, which is not far from teh 
house.

Yours,
Dora Smith
Austin, TX
tiggernut24 at yahoo.com

----- Original Message ----- 
From: "Mr EMan" <mstreman53 at yahoo.com>
To: "Rockhounds at drizzle.com: A mailing list for rock and gem collectors" 
<rockhounds at lists.drizzle.com>
Sent: Thursday, November 13, 2008 5:35 PM
Subject: Re: [Rockhounds] What is this rock?

>A note on the acid reaction to what appears to be gneiss cobbles from The 
>Adarondack Mtns.
>
> Until 13-12,000 years ago, this region of the North East US was covered by 
> an ice cap.  That scraping shoving glacial process, produces a high 
> concentration solution of CaCO3. This is an excellent cementing agent and 
> will cement smaller cobbles, pebbles and sands together. It also leaves a 
> residue in cracks which may be the source of the fizzing you tested for.
>
> I have several examples of granite cobbles covered in fluorescing 
> aragonite. In fact any rock from the region can be found somewhere with a 
> coating of aragoinite.  I surmise the reaction you had to hydrocloric acid 
> was limited to this aragonite. Yes-- this example is apparently gneiss and 
> neither sandstone nor granite.  BUT I loved the fact that you set about 
> using the tools, logic, and followed a process to ID the sucker!!!  For 
> that my hat is off to Dora
>
> Elton
>
> --- On Tue, 11/11/08, Carolyn Reynard <sunstone3 at hvc.rr.com> wrote:
>
>> From: Carolyn Reynard <sunstone3 at hvc.rr.com>
>> Subject: Re: [Rockhounds] What is this rock?
>> To: "Dora Smith" <tiggernut24 at yahoo.com>, "Rockhounds at drizzle.com: A 
>> mailing list for rock and gem collectors" <rockhounds at lists.drizzle.com>
>> Date: Tuesday, November 11, 2008, 10:43 PM
>> Dora, Your rocks certainly look like gneiss. The banding of
>> light and dark
>> minerals is typical.  The dark mineral(s)
>> would be bioitie or hornblende. The light mineral(s) would
>> be quartz and/ or
>> feldspar.  One would not expect any reaction to HCL. Rinse
>> them well, they
>> probably won't be a problem in a fish tank.
>>
>> I'm not familiar with an Adirondack smell. Your Austin
>> smell would seem to
>> be like an earthy moldy clay odor.
>>
>> Carolyn Reynard
>> Poughkeepsie, NY
>>
>>
>> ----- Original Message ----- 
>> From: "Dora Smith" <tiggernut24 at yahoo.com>
>> To: <rockhounds at lists.drizzle.com>
>> Sent: Tuesday, November 11, 2008 10:05 PM
>> Subject: [Rockhounds] What is this rock?
>>
>>
>> I asked my sister to bring me home some Adirondack granite
>> from our family
>> home for my fish tank, and she brought me these two rocks.
>>  Photos are at
>> http://good-times.webshots.com/album/568626982hMlTIK
>>
>> They look sedimentary; they are banded.  They are heavy and
>> softer than
>> granite ought to be; they scratch with a knife.  They react
>> weakly with 10%
>> hydrochloric acid (toilet bowl cleaner).  Some parts of the
>> rock definitely
>> fizz, especially if the rock is hot, but not as vigorously
>> as limestone.
>> Sometimes acid toilet bowl cleaner leaves behind a rough
>> residue of large
>> sand grains easily scratched off.  They do not fizz with
>> vinegar.
>>
>> The rock smells distinctly like Adirondack rock and
>> distinctly NOT like
>> Austin rock.  In Austin nearly all rock is soft limestone,
>> and it always
>> smells yucky.   There is no other way to describe it.   The
>> soil smells the
>> same sort of yucky.
>>
>> I thought they were limestone until I saw photos of gneiss;
>> they look alot
>> like gneiss.  but from what I am reading gneiss is not made
>> from limestone.
>> Usually it is made of solid silicate rock that is already
>> hard and durable.
>>
>> Can silicate react with hydrochloric acid?
>>
>> What is this rock?
>>
>> If it is limestone based, is it hard enough not to throw
>> off the chemistry
>> of my fresh water tropical fish tank?   In Austin the water
>> is hard when it
>> is taken from the river but it is treated with water
>> softeners.
>>
>> Yours,
>> Dora Smith
>>
>> Yours,
>> Dora Smith
>> Austin, TX
>> tiggernut24 at yahoo.com
>>
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