Autunite, A Naturally Occurring Fluorescent and Radioactive Mineral Phosphate
Autunite has been a popular mineral for collectors for several reasons. One being, it naturally fluoresces under exposure to ultraviolet light. And two, because it contains Uranium which is commonly used in manufacturing of radioactive weapons such as atomic weaponry.
Uranium among two other isotopes is what gives Autunite its radioactivity. Radioactivity, as described by B. B. Boltwood, is the spontaneous decay of an atom's nucleus that forms a new nucleus. So, as it decays, the atom gives off neutrons or protons, along with energy in the form of radiation. B. B. Boltwood devised a method of dating rocks by measuring radioactive decay.
Uranium-238 eventually decays into the heavy metal, lead. And it has a half life of about 4.5 billion years. This means that after 4.5 billion years, a single Uranium-238 atom will decay about fifty percent of the time.
Autunite is known for its striking yellowish green color which is similar to a bright lemon-lime pigment. It has what's known as tabular crystals which are thin, twinned crystals that are clearly visible by eye. Technically, Autunite has a Tetragonal crystal structure with a vitreous to pearly luster, and is translucent to transparent.
The properties of Autunite are not unlike other phosphates. It has a hardness of 2 to 2 1/2 on the Moh's scale and has received its name for the location in which it was discovered; Autun, France. Autunite is actually a secondary mineral that has been created by the oxidation of Uranium ore in an oxidation zone. It is also naturally occurring in hydrothermal veins and pegmatites which can be found in countries such as England, Japan, Germany, India, the U.S, Brazil and Australia.
For collectors who are looking to add Autunite to their collections, caution must be taken to properly store the mineral without causing harm to others due to its high concentration of radioactivity.
Autunite is recommended to be stored in a well-ventilated location outside of the physical residence. If Autunite is stored in a sealed container, radon gas can build up in concentration which can be hazardous to the health of those handling it, especially when opening the sealed container who would be in direct proximity of the gas.
Museums that store and feature Autunite do so with specimens that have been lightly heat treated. When the mineral is heated, it changes structure from tetragonal to an orthrombic meta-autunite which is due to the loss of moisture or water in the mineral. Most museums feature these types of specimens partly converted minerals.