Hence, the Rb/Sr ratio in residual magma may increase over time, resulting in rocks with increasing Rb/Sr ratios with increasing differentiation. Typically, Rb/Sr increases in the order plagioclase, hornblende, K-feldspar, biotite, muscovite.Therefore, given sufficient time for significant production (ingrowth) of radiogenic For example, consider the case of an igneous rock such as a granite that contains several major Sr-bearing minerals including plagioclase feldspar, K-feldspar, hornblende, biotite, and muscovite.Thus, although "extinct", these nuclides are present in meteorites, but produced by a more recent process.
The slope of the line dictates the age of the sample.Trees undergo spurts in growth in the spring and summer months while becoming somewhat dormant in the fall and winter months.When a tree is cut down, these periods are exhibited in a cross section of the trunk in the form of rings.After the second half-life has elapsed, yet another 50% of the remaining parent isotope will decay into daughter isotopes, and so on.For all practical purposes, the original isotope is considered extinct after 6 half-life intervals. A small portion of a meteorite is vaporized in the device forming ions.Meteorites are among the oldest objects we know about - formed about 4.5 billion years ago. This article describes the principles and methods used to make that determination.There are well-known methods of finding the ages of some natural objects.However, because Rb substitutes for K in minerals and these minerals have different K/Ca ratios, the minerals will have had different Rb/Sr ratios.During fractional crystallization, Sr tends to become concentrated in plagioclase, leaving Rb in the liquid phase.Conversely, these fluids may metasomatically alter a rock, introducing new Rb and Sr into the rock (generally during potassic alteration or calcic (albitisation) alteration.Rb-Sr can then be used on the altered mineralogy to date the time of this alteration, but not the date at which the rock formed.