Ask GeoMan...

When you say pass or fail the 'fizz test', do you mean if it fizzes it passes or if it doesn't it passes? Also is a Marble rock considered a feldspar on the Mohs Hardness scale. My rock is white. My teacher says she thinks it is marble. My rock did not fizz when I poured vinegar on it, and I can scratch hard glass. A steel knife didn't scratch it.

--- Jason; Tulsa, OK


"Pass" means that it fizzes, and is therefore composed of calcium carbonate. Marble is a carbonate rock, and therefore is soft (less than your knife) and fizzes. Sometimes you may have to grind up some of the sample into powder to increase the surface before you can see the reaction - especially when using a weak acid like vinegar. Feldspar is a silicate mineral not composed of calcium carbonate. Therefore it is harder than your knife, and doesn't fizz. Only minerals are used on the Mohs scale, so marble isn't there (but feldspar is). I'm not sure what you have - sounds too hard for marble, but you will need to do additional testing to make a determination beyond that.


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