[Rockhounds] What is this rock?

[Dora Smith]

I don't think so.  As I recall, dolomite is limestone with magnesium in it.   It is found around Austin, and is higher quality than most limestone found around here, and as I recall it reacts pretty strongly with HCl.   It ahs been a few years since I did my Great Limestone Survey, and I had to travel some distance and search to fnid dolomite.

Dolomite is very hard, very fine, and a distinctive tan-yellow color.   This rock does not have dolomite.

Yours,
Dora Smith
Austin, TX
tiggernut24 at yahoo.com
  ----- Original Message ----- 
  From: J Bryan Kramer 
  To: Dora Smith ; Rockhounds at drizzle.com: A mailing list for rock and gem collectors 
  Sent: Tuesday, November 11, 2008 9:47 PM
  Subject: Re: [Rockhounds] What is this rock?


  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

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  "The thunderbolt falls on an inch of ground; but the light of it fills the horizon."

                         Ralph Waldo Emerson

  J Bryan Krämer
  North Florida, USA
  photos at:
  http://pbase.com/photoburner


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