If left at low surface temperatures for a geologically long time, the radioactivity within the crystal can destroy the crystal lattice structure, whereas at higher temperatures this process is self-annealing.
In fact, when examined by X-ray methods, some zircons have no detectable structure, indicating that at least 25 percent of the initial atoms have been displaced by Potassium–argon methods) in biotite can cause lead to be lost in some grains.
Radioactive decay Radioisotopic dating relies on the process of radioactive decay, in which the nuclei of radioactive atoms emit particles.
For example, as shown at left below, uranium-235 has a half-life of 704 million years.
That means that in 704 million years, one gram of uranium will be reduced to ½ gram of uranium.
crystal structure allows a small amount of tetravalent uranium to substitute for zirconium but excludes with great efficiency the incorporation of lead.
(It might be said that one begins with an empty box.) Second, zircon, once formed, is highly resistant to change and has the highest blocking temperature ever observed.
In one sample it was determined that a sandstone that underlies most of the province of Nova Scotia in Canada was probably originally deposited off the coast of North Africa and thrust over the continent before the opening of the Atlantic Ocean.