Yes it is true… Granite and marble do emit tiny but noticeable amount of radiation in different proportions.
Both granite and marble are naturally occurring materials that were formed millions of years ago similar to minerals.
Generally these substances contain traces of radioactive elements like uranium, thorium and their daughter products like radium polonium and radon.
What is the amount of radiation emitted?
An estimated composition would be of 60 to 70 atoms of uranium and about 10 atoms of thorium will be emitted as radiation every second per 1 kilogram of granite.
On the other hand the emission in marble due to these radioactive materials is one tenth of granite.
The amount of radioactivity emitted by these rocks varies through different geographical locations. Granites from India and Egypt have very low emanation rates and are by far the best in the world in this regard.
Is it dangerous?
It is relieving to hear that the radioactive levels in granite and marble are too small to be of any concern, but all construction materials, in general emit a small amount of radon gas which is radioactive, and can easily accumulate in poorly ventilated buildings. Inhaling the accumulated radon could give rise to small degree of radiation exposure.
Hence to prevent these radiation exposures it is advised to have a better ventilation.
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