Baddeleyite

Baddeleyite
Baddeleyite from Phalaborwa, South Africa
General
Category	Oxide mineral
Formula (repeating unit)	Zirconium dioxide (ZrO2)
Strunz classification	4.DE.35
Dana classification	04.04.14.01
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	P21/c
Unit cell	a = 5.1505 Å, b = 5.2116 Å, c = 5.3173 Å, β = 99.23°; Z = 4
Identification
Color	Colorless to yellow, green, greenish or reddish brown, brown, iron-black
Crystal habit	Tabular prismatic, radially fibrous in botryoidal masses
Twinning	Ubiquitous polysynthetic on {100} and {110}
Cleavage	{001} distinct
Fracture	Irregular uneven to subconchoidal
Tenacity	Brittle
Mohs scale hardness	6.5
Luster	Greasy to vitreous
Streak	White
Diaphaneity	Transparent to translucent
Specific gravity	5.5–6
Optical properties	Biaxial (–)
Refractive index	nα = 2.130 nβ = 2.190 nγ = 2.200
Birefringence	δ = 0.070
Pleochroism	X = yellow, reddish brown, oil-green; Y = oil-green, reddish brown; Z = brown, light brown
2V angle	Measured: 30° to 31°
Dispersion	r > v, rather strong
Other characteristics	Blue-green cathodoluminescence
References

Baddeleyite is a rare zirconium oxide mineral (ZrO₂ or zirconia), occurring in a variety of monoclinic prismatic crystal forms. It is transparent to translucent, has high indices of refraction, and ranges from colorless to yellow, green, and dark brown. See etymology below.

Baddeleyite is a refractory mineral, with a melting point of 2700 °C. Hafnium is a substituting impurity and may be present in quantities ranging from 0.1 to several percent.

It can be found in igneous rocks containing potassium feldspar and plagioclase. Baddeleyite is commonly found with zircon (ZrSiO₄), yet it forms in places with lower silica content, such as mafic rocks. This is because baddeleyite tends to become zircon where there is higher silica content, hence why both minerals can be found together. It belongs to the monoclinic-prismatic class, of the P2₁/c crystal system. It has been used for geochronology.

Baddeleyite was first found in Sri Lanka in 1892. It can be found in numerous terrestrial and lunar rocks. Some of these terrestrial rocks are carbonatite, kimberlite, alkaline syenite, some rocks of layered mafic intrusions, diabase dikes, gabbroid sills and anorthosite. Some examples of lunar rocks are tektites, meteorites and lunar basalt. Studies have shown that zircon and baddeleyite can be recovered from some anorthositic rocks in Proterozoic anorthosite complexes. Places where these Proterozoic anorthosite complexes can be found are: the Laramie Anorthosite Complex in Wyoming, the Nain and Grenville provinces of Canada, the Vico Volcanic Complex in Italy, and Minas Gerais and Jacupiranga, São Paulo, Brazil. Baddeleyite forms in igneous rocks low in silica, it can be found in rocks containing potassium feldspar and plagioclase. It has been observed in thin section that baddeleyite forms within plagioclase grains. Associated minerals include ilmenite, zirkelite, apatite, magnetite, perovskite, fluorite, nepheline, pyrochlore and allanite.