Granite Countertops and Radiation

The information about granite and radioactivity in granite.

>Granite Overview
>Radioactivity and Granite
>Testing

Granite Overview :

In geological terms, granite is an igneous rock, meaning it was formed when magma (molten rock) cooled very slowly until it solidified in a process that can take many of thousands, or even millions of years. Since the rock forms so slowly, minerals have a long time to grow into the crystals that give granite its decorative appearance. Depending on the crystals that are formed, granite can come in a wide range of colors. This and other factors, make granite a popular building material in homes and buildings.

Radiation from Granite :

Any naturally formed rock material has the potential of containing varying amounts of naturally occurring radiation. Natural radioactive elements like uranium, radium, and thorium can be present in a wide number of minerals that appear as crystals in granite from around the world. So, it is not unusual for materials such as granite to have some amount of radioactivity (emissions of alpha or beta particles or gamma rays). Depending on the composition of the molten rock from which they formed, some pieces of granite can exhibit more radioactivity than others.
When present, certain radioactive elements in granite will decay into radon, a colorless, odorless, radioactive gas which may be released from the granite over time. You can see in the diagram below how the decay of Uranium-238 (a radioactive element) produces Radon-222 gas:

However, since granite is generally not very porous, less radon is likely to escape from it than from a more porous stone such as sandstone. It’s important to know that radon originating in the soil beneath homes is a more common problem and a far larger public health risk than radon from a granite countertop or other building materials. Also, any radon from granite in kitchens or bathrooms is likely to be somewhat diluted in the typical home since those rooms are among the most ventilated.

Testing :

Radiation coming from granite countertops results from natural radioactive material in the granite. Identifying the presence and concentration of radioactive elements in granite requires expensive and sophisticated portable instruments or laboratory equipment. These instruments and equipment require proper calibration, and interpretation of their readings requires a knowledgeable and trained user. At this time, there is no generally accepted home testing protocol for radiation in granite countertops.