Changes

===Problems and exceptions===

===Problems and exceptions===

* ''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.