Changes

* ''Clay minerals''. Illite clays are rich in potassium, whereas smectite and kaolinite contain thorium. The thorium to potassium ratio can distinguish illitic from smectitic shales and so provide a correlation tool.

* ''Clay minerals''. Illite clays are rich in potassium, whereas smectite and kaolinite contain thorium. The thorium to potassium ratio can distinguish illitic from smectitic shales and so provide a correlation tool.

* ''Organic-rich rocks''. In shales, uranium enrichment is usually associated with organic content and can be a tool for identifying oil source beds. Quantitative relationships between uranium and organic content have been reported, but tend to be inconsistent.

* ''Organic-rich rocks''. In shales, uranium enrichment is usually associated with organic content and can be a tool for identifying oil source beds. Quantitative relationships between uranium and organic content have been reported, but tend to be inconsistent.

* ''Mica sand''. Richly micaceous sands (such as the Rannoch unit of the Brent Sand in the North Sea) appear shaly on gamma ray logs, but can be distinguished because the radiation is all from potassium.

* ''Mica sand''. Richly micaceous sands (such as the Rannoch unit of the Brent Sand in the [[North Sea]]) appear shaly on gamma ray logs, but can be distinguished because the radiation is all from potassium.

* ''“Hot” dolomite''. This type of dolomite can be distinguished from shale because the gamma rays are principally from uranium. The chemical relationship between uranium and the dolomite is unknown.

* ''“Hot” dolomite''. This type of dolomite can be distinguished from shale because the gamma rays are principally from uranium. The chemical relationship between uranium and the dolomite is unknown.

* ''Natural fractures''. Soluble uranium in pore water often precipitates on open fractures, so thin intervals with high uranium count (a “spiky” log) may mark a fractured interval.

* ''Natural fractures''. Soluble uranium in pore water often precipitates on open fractures, so thin intervals with high uranium count (a “spiky” log) may mark a fractured interval.