Pyrochlore

Pyrochlore
Pyrochlore from Russia
General
Category	Oxide mineral
Formula (repeating unit)	(Na,Ca)2Nb2O6(OH,F)
IMA symbol	Pcl[1]
Strunz classification	4.DH.15
Dana classification	08.02.01.01 Pyrochlore group
Crystal system	Isometric
Crystal class	Hexoctahedral (m3m) H-M symbol: (4/m 3 2/m)
Space group	Fd3m (No. 227)
Unit cell	a = 10.41(6) Å, Z = 8
Identification
Color	Black to brown, chocolate-brown, reddish brown, amber-orange, red-orange
Crystal habit	Typically octahedra, disseminated granular, massive
Twinning	111 rare
Cleavage	111 indistinct, may be a parting.
Fracture	Subconchoidal to uneven, splintery
Tenacity	Brittle
Mohs scale hardness	5.0–5.5
Luster	Vitreous to resinous
Streak	White
Diaphaneity	Subtranslucent to opaque
Specific gravity	4.45 to 4.90
Optical properties	Isotropic, weak anomalous anisotropism
Refractive index	n = 1.9–2.2
Other characteristics	Radioactive, often metamict
References	[2][3][4][5]

Pyrochlore (Na,Ca)₂Nb₂O₆(OH,F) is a mineral group of the niobium end member of the pyrochlore supergroup. Pyrochlore is also a term for the crystal structure Fd3m. The name is from the Greek πῦρ, fire, and χλωρός, green because it typically turns green on ignition in classic blowpipe analysis.^[4]