Changes

* ''Radioactive minerals'' in sands, especially K-feldspar, zircon, and mica, can raise sand readings as high as adjacent shales. Gamma ray logs may be useless in immature sands derived from [[basement]] terranes. However, beach placers rich in zircon may be valuable correlative markers if not mistaken for shale.

* ''Radioactive minerals'' in sands, especially K-feldspar, zircon, and mica, can raise sand readings as high as adjacent shales. Gamma ray logs may be useless in immature sands derived from [[basement]] terranes. However, beach placers rich in zircon may be valuable correlative markers if not mistaken for shale.

* ''“Hot” dolomite'', especially common in the Permian basin in the United States, may have gamma ray values up to 200 API units, resembling shale.

* ''“Hot” dolomite'', especially common in the [[Permian basin]] in the United States, may have gamma ray values up to 200 API units, resembling shale.

* ''Radioactive (KCl) muds'' raise the baseline gamma ray zero reading so that apparent values for all rock types are increased, sometimes by about 20 API units.

* ''Radioactive (KCl) muds'' raise the baseline gamma ray zero reading so that apparent values for all rock types are increased, sometimes by about 20 API units.

* ''Evanescent high gamma ray'' readings in sands, present on one logging run but vanished some weeks later, have been observed especially in steamflood conditions. While remaining enigmatic, these may be due to concentrations of radon in the pore space.

* ''Evanescent high gamma ray'' readings in sands, present on one logging run but vanished some weeks later, have been observed especially in steamflood conditions. While remaining enigmatic, these may be due to concentrations of radon in the pore space.