Reidite

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.

Reidite
General
Category	Zircon group
Formula	ZrSiO4
IMA symbol	Rei[1]
Strunz classification	9.AD.45
Crystal system	Tetragonal
Crystal class	Dipyramidal (4/m) H-M symbol: (4/m)
Space group	I41/a
Unit cell	a = 4.738, c = 10.506 [Å], Z = 4
Identification
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.
Cleavage	None
Fracture	Irregular/uneven
Tenacity	Brittle
Mohs scale hardness	7.5
Luster	Adamantine
Streak	White
Diaphaneity	Translucent
Specific gravity	5.16
Optical properties	Uniaxial (+)
Refractive index	nω=1.64, nε=1.655
Birefringence	0.0150
Pleochroism	None
References	[2][3]

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;^[4] Rock Elm Crater in Wisconsin;^[5] Dhala Crater in India;^[6] Stac Fada in Scotland; Haughton in Canada; Steen River in Canada, and Rochechouart in France. Reidite has also been found in one lunar meteorite.^[7]

Name origin and discovery

Reidite is named after Alan F. Reid, the scientist who first synthesized it during high-pressure experiments in the laboratory in 1969.^[8]

Reidite was first discovered in natural samples by B.P. Glass and Shaobin Liu in 2001.^[9]

Occurrence

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.^[10] 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.^[11]

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.^[12]

Related silica minerals

Relationship of Reidite to Other Specimens

9.AD.25	Uvarovite	Ca3Cr2(SiO4)3
9.AD.25	Wadalite	(Ca,Mg)6(Al,Fe3+)4((Si,Al)O4)3O4Cl3
9.AD.25	Holtstamite	Ca3(Al,Mn3+)2(SiO4)2(OH)4
9.AD.25	Kerimasite	Ca3Zr2(SiO4)(Fe3+O4)2
9.AD.25	Toturite	Ca3Sn2(SiO4)(Fe3+O4)2
9.AD.25	Momoiite	(Mn2+,Ca)3V23+(SiO4)3
9.AD.25	Eltyubyuite	Ca12Fe103+Si4O32Cl6
9.AD.25	Hutcheonite	Ca3Ti2(SiAl2)O12
9.AD.30	Coffinite	(U4+,Th)(SiO4)1-x(OH)4x
9.AD.30	Hafnon	HfSiO4
9.AD.30	Thorite	(Th,U)SiO4
9.AD.30	Zircon	ZrSiO4
9.AD.30	Stetindite	Ce4+SiO4
9.AD.35	Huttonite	ThSiO4
9.AD.35	Tombarthite-(Y)	Y4(Si,H4)4O12−x(OH)4+2x
9.AD.40	Eulytine	Bi4(SiO4)3

See also

• List of minerals