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Natural Radiation

Granite is a normal, geological, source of radiation in the natural environment. Granite has around 10 to 20 parts per million of uranium. By contrast, black granite (typically actually a tonalite, gabbro or diorite) has 1 to 5ppm uranium, and limestones and sedimentary rocks usually equally low.

Many large granite plutons are the sources for palaeochannel-hosted or roll front uranium ore deposits, where the uranium washes into the sediments from the granite uplands and associated, often highly radioactive, pegmatites.

In buildings constructed primarily from natural granite, it is possible to be exposed to approximately 200 mrems per year. 1

Granite could be considered a potential natural radiological hazard as, for instance, villages located over granite may be susceptible to higher doses of radiation than other communites. 2 Cellars and basements sunk into soils formed over or from particularly uraniferous granites can become a trap for radon gas, which is heavier than air.

However, in the majority of cases, although granite is a significant source of natural radiation as compared to other rocks it is not often an acute health threat or significant risk factor. Various resources from national geological survey organisations are accessible online to assist in assessing the risk factors in granite country and design rules relating, in particular, to preventing accumulation of radon gas in enclosed basements and dwellings.

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