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Metamictization (sometimes called metamiction) is a natural process resulting in the gradual and ultimately complete destruction of a mineral's crystal lattice, leaving the mineral amorphous. Affected material is therefore described as metamict.Certain minerals occasionally contain interstitial impurities of radioactive compounds and it is the alpha radiation emitted from these compounds that is responsible for degrading a mineral's crystal structure through internal bombardment. Effects of metamictization are extensive: other than negating any birefringence previously present, the process also lowers a mineral's refractive index, hardness, and specific gravity. The mineral's colour is also affected: metamict specimens are usually green or brown. Further, metamictization diffuses the bands of a mineral's absorption spectrum. Curiously and inexplicably, the one attribute which metamictization does not alter is dispersion. All metamict materials are themselves radioactive, some dangerously so.
An example of a metamict mineral is zircon. The presence of the uranium mineral coffinite and the thoriumThorium is a chemical element in the periodic table that has the symbol Th and atomic number 90. Notable characteristics Thorium is a naturally occurring, slightly radioactive metal. When pure, thorium is a silvery white metal that retains its lustre for mineral thoriteThorite (Th,U)SiO, is a rare silicate of thorium that crystallizes in the tetragonal system and isomorphous with zircon. It is the most common mineral of thorium and is nearly always strongly radioactive. It was named in 1829 to reflect its thorium conten are responsible for the radiation damage in this case. Unaffected specimens are termed high zircon while metamict specimens are termed low zircon. Specimens falling between the two extremes are termed intermediate. Other minerals known to undergo metamictization include ekanite and titaniteTitanite or sphene is a calcium titanium silicate mineral according to the chemical formula CaTiSiO. Trace impurities of iron and aluminium are invariably present. Also commonly present are rare earths including cerium and yttrium. Titanite, which is name. Ekanite is almost invariably found completely metamict as thorium and uranium are part of its essential chemical compositionThe chemical composition of a substance refers to the elements of which the substance is composed. For example, common table salt is composed of sodium and chlorine, but this familiar chemical compound is also found in halite..
Metamict minerals can have their crystallinity and properties restored through prolonged annealingThe word anneal has several meanings: In metallurgy and materials science annealing is a heat treatment wherein the microstructure of a material is altered, causing changes in its properties such as strength and hardness. Typically, this results in soften.
