The uranium content of the sample has to be known, but that can be determined by placing a plastic film over the polished slice of the material, and bombarding it with slow neutrons. This temperature is what is known as closure temperature and represents the temperature below which the mineral is a closed system to isotopes. At any stage in the crystallization process the melt might be separated from the solid portion of the magma. I'm guessing a little bit here. I'd like to know how often this happens, in any case, especially on the geologic column of Cambrian and above. Some of the patterns that are produced may appear to give valid radiometric dates. As is often the case, there are problems on both sides.
It is an accurate way to date specific geologic events.
It is a bit in between. Uranium—lead dating is often performed on the mineral zircon ZrSiO 4though it can be used on other materials, such as baddeleyiteas well as monazite see: For example, the age of the Amitsoq gneisses from western Greenland was determined to be 3. Earlier, I indicated how crystals can have defects or imperfections in which small amounts of magma can be trapped. It turns out that uranium in magma is typically found in the form of uranium dioxide, with a melting point of degrees centrigrade. The results from all of the laboratories were remarkably consistent with the measured ages ranging only from
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