Reidite is a rare polymorph of ZrSiO4 created when zircon experiences high pressure and temperature. Reidite is denser than zircon and has the same crystal structure as scheelite. All natural occurrences of reidite are associated with meteorite impact events.
|Crystal class||Dipyramidal (4/m) |
H-M symbol: (4/m)
|Unit cell||a = 4.738, c = 10.506 [Å], Z = 4|
|Formula mass||183.31 g/mol|
|Color||Colorless to white|
|Crystal habit||Epitaxial - crystallographic alignment with a precursor mineral, occurs as inclusions in other minerals.|
|Mohs scale hardness||7.5|
|Optical properties||Uniaxial (+)|
|Refractive index||nω=1.64, nε=1.655|
On Earth, reidite has been reported from ten impact structures: the Chesapeake Bay Crater in Virginia; Ries Crater in Germany; Xiuyan Crater in China; Woodleigh Crater in Western Australia; Rock Elm Crater in Wisconsin; Dhala Crater in India; Stac Fada in Scotland; Haughton in Canada; Steen River in Canada, and Rochechouart in France. Reidite has also been found in one lunar meteorite.
Reidite is named after Alan F. Reid, the scientist who first synthesized it during high-pressure experiments in the laboratory in 1969.
Reidite was first discovered in natural samples by B.P. Glass and Shaobin Liu in 2001.
Reidite is formed from zircon above ~30GPa in shock recovery experiments. However, the temperatures generated during meteorite impacts are much higher, and reidite can be formed down to ~9GPa under natural impact conditions. Reidite has been found in lamellar, granular, and dendritic forms within host zircon, typically making up less than 10% of the grain. Reidite from Rochechouart impact structure has also been reported as bladed, wedged, and massive.
Libyan desert glass may show lattice deformation in zircon that is interpreted as evidence of this material having previously contained reidite, and as such constitutes strong evidence for its impact origin.