[Rockhounds] What is this rock?

[Pmodreski at aol.com]

I'll agree too, they certainly look like gneiss.
 
Some gneisses can contain calcite; the rock can be intermediate in  
composition between a marble and a silicate gneiss.  And yes, it's  certainly true that 
dolomite would react weakly with acid.  And a regular  gneiss (made of 
quartz, feldspar, etc.) would not be scratched by a knife.   It sounds like your 
rock is perhaps as I say, a banded, gneissic marble; or one  could say, a 
calcareous gneiss--such things exist, it might not be unreasonable  to find them 
somewhere in the Adirondacks.
 
I just did a little Googling on this (Adirondack marble), and yes, there  are 
indeed lots of marbles in the Adirondacks.  There are even the  "Adirondack 
Marble Caves"!  And graphite occurs in some of these marbles,  so some of the 
dark grains in your rocks may be graphite.  I would now say  your rocks are 
probably a gneissic, impure marble.  Which means, as a  marble, it would have a 
slight, slow solubility in water and a very slight  tendency to dissolve in 
your fish tanks, but probably very slowly, much slower  than your local Texas 
limestone would.
 
Pete Modreski
 
 
In a message dated 11/11/2008 8:48:12 P.M. Mountain Standard Time,  
codeburner at gmail.com writes:

Doesn't  dolomite react weakly with acid?

BK

On Tue, Nov 11, 2008 at  22:44, Dora Smith <tiggernut24 at yahoo.com> wrote:

> 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
>>
>> 

**************AOL Search: Your one stop for directions, recipes and all other 
Holiday needs. Search Now. 
(http://pr.atwola.com/promoclk/100000075x1212792382x1200798498/aol?redir=http://searchblog.aol.com/2008/11/04/happy-holidays-from
-aol-search/?ncid=emlcntussear00000001)


--- StripMime Report -- processed MIME parts ---
multipart/alternative
  text/plain (text body -- kept)
  text/html
---