[Rockhounds] What is this rock?

[Dora Smith]

I actually scrubbed them well in dish washer detergent, soaked in bleach, 
and boiled before testing them with toilet bowl cleaner.

What do you make of the fact that they do react with HCl?  And should gneiss 
scratch with a knife?

Yours,
Dora Smith
Austin, TX
tiggernut24 at yahoo.com
----- Original Message ----- 
From: "Carolyn Reynard" <sunstone3 at hvc.rr.com>
To: "Dora Smith" <tiggernut24 at yahoo.com>; "Rockhounds at drizzle.com: A mailing 
list for rock and gem collectors" <rockhounds at lists.drizzle.com>
Sent: Tuesday, November 11, 2008 9:43 PM
Subject: Re: [Rockhounds] What is this rock?


> 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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