What could be causing orange, reddish, brown stuff to come off my granite countertop

[Andrea]

What could be causing orange, reddish, brown stuff to come off my granite countertop in the kitchen when it is wiped down?

Could this be dangerous?

It is about 13 years old, and it gets cleaned and wiped down daily.

[home improvement guy]

Granite is a hard, nonporous mineral similar to marble and, depending on its source, can be stained, chipped or discolored. Granite is softer than marble and consists mainly of quartz and feldspar rocks - the two most common rocks on earth. Granite also contains mica and amphibole minerals - "a group of generally dark colored minerals often containing ions or magnesium that can be green, black, white, yellow, blue or brown."

Granite is impervious to water, but the polished surface may be exposing one or more of these minerals that can oxidize and change color when exposed to water. Granite and marble can also be etched slightly by mild acidic fruits and juices or discolored from a hot pan set out on the counter to cool. My research indicates the discoloration is simply a part of the countertop's structure and that it may, depending on the depth of the exposed mineral, go away after years of use.

Try using a commercial cleaner or even a polish to protect the surface from water and spills. I do not believe the color change presents any dangers to humans and is most likely a type of rust or oxidation, but if you have any doubts, take a sample to your family doctor for further investigation.

A 2008 study of 39 different sizes and types of granite countertops (initiated and paid for by the Marble Institute of America) by Environmental Health & Engineering showed that all of the 39 granite slabs measured for the study showed radiation levels well below the European Union safety standards and radon emission levels well below the average outdoor radon concentrations in the U.S. You can do a radon test in your kitchen by purchasing a radon test kit from one of the major hardware stores.

Leave the test kit in place for several months before sending it to the radon test kit's laboratory for analysis. You can read more about radon gas at the EPA website www.epa.gov.