Metamict

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Metamict (formerly also pyrognomic ) is the name of a crystal whose crystal structure has been destroyed by radioactivity .

In crystals with a relatively high content of radioactive elements, the atoms are knocked out of their lattice positions due to the ionizing radiation and do not return to their original position. This means that the previously crystalline state changes into an amorphous , glass-like state. In compounds with a less pronounced salt character , the negative effect on the crystal lattice is particularly high.

The material mostly retains its external, crystalline appearance, but density and transparency decrease and the color changes from green or brown to an opaque black. In addition, the gloss decreases and becomes pitch-like . The cleavage is also lost, but a conspicuously scalloped fracture appears .

Metamorphosed crystals are also referred to as isotropic or isotropic crystals, since their originally direction-dependent ( anisotropic ) properties such as hardness and refractive index now become independent of direction.

The isotropy can often be "repaired" by heating. The heat causes the atoms to return to their place, whereby energy is also released, which can be expressed by glowing (see thermoluminescence ). The so-called Wigner energy is based on the isotropy of graphite moderators.

Examples of metamiked crystal finds in minerals include allanite , blomstrandin , betafit , columbite , euxenite , fergusonite , gadolinite , pyrochlore , samarskite , thorite and zircon . Other minerals such as uraninite , thorianite and yttrotitanite are often only slightly isotropic despite their high content of uranium and thorium . It is therefore assumed that their crystal lattices have good regenerative properties.

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