[Rockhounds] What is this rock?

[GREGORY WEISBROD]

Dora,  My inexpert guess is they are a marble calc-silicate rock.  The reaction with warm HCl is characteristic.Marble being metamorphic the bands probably indicate flow, maybe on account of a few miles of glacier piledon top.  The texture is due to the sand and other stuff caught up with the original limestone.  If I had realvaluable fish, I might be leery of environmental impact, not from the mineral but possible disease organisms.I would take my rocks out to grill on low for an hour before cooling and introducing to the aquarium.Good luck, Greg 
 
> From: tiggernut24 at yahoo.com> To: rockhounds at lists.drizzle.com> Date: Tue, 11 Nov 2008 21:05:09 -0600> 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> > --- StripMime Report -- processed MIME parts ---> multipart/alternative> text/plain (text body -- kept)> text/html> ---> -- > _______________________________________________> Rockhounds at drizzle Mailing List> Subscription Services:> http://lists.drizzle.com/mailman/listinfo/rockhounds> List Home Page, with a link to the List Usage Policy:> http://www.eclecticlapidary.com/Rockhounds/index.html

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