Tyuyamunite (pronounced tuh-YOO-ya-moon-ite) is a very rare uranium mineral with formula Ca(UO₂)₂V₂O₈·(5–8)H₂O. It is a member of the carnotite group. It is a bright, canary-yellow color because of its high uranium content. Also, because of tyuyamunite's high uranium content, it is radioactive.^[6] It was named by Konstantin Avtonomovich Nenadkevich, in 1912, after its type locality, Tyuya-Muyun, Fergana Valley, Kyrgyzstan.^[3]

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Tyuyamunite
General
Category	Vanadate mineral
Formula (repeating unit)	Ca(UO2)2V2O8·(5–8)H2O
IMA symbol	Tyu[1]
Strunz classification	4.HB.25
Dana classification	40.2a.26.1
Crystal system	Orthorhombic
Crystal class	Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m)
Space group	Pnna
Unit cell	a = 10.63 Å, b = 28.36 Å c = 20.4 Å; Z = 4
Identification
Colour	Canary yellow, lemon-yellow; greenish yellow (upon exposure to sunlight)
Crystal habit	Platy crystals often in radiating sprays, coatings, massive
Cleavage	Perfect on {001}, micaceous; distinct on {100} & {010}
Mohs scale hardness	1+1⁄2 – 2
Lustre	Adamantine, waxy, pearly on {101}, dull
Streak	Yellow
Diaphaneity	Translucent to opaque
Specific gravity	3.57 – 4.35
Optical properties	Biaxial (−)
Refractive index	nα = 1.675 nβ = 1.860 – 1.870 nγ = 1.885 – 1.895
Birefringence	0.210 – 0.220
Pleochroism	weak: X = nearly colourless, Y = pale canary yellow, Z = canary yellow
2V angle	30° to 45°
Dispersion	none
Other characteristics	Radioactive
References	[2][3][4][5]

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Tyuyamunite is formed by the weathering of uraninite, a uranium-bearing mineral. Tyuyamunite, being a hydrous mineral, contains water. Yet when it is exposed to the atmosphere it loses its water. This process changes tyuyamunite into a different mineral known as metatyuyamunite^[6] Ca(UO₂)₂(VO₄)₂·3-5H₂O.^[7]