Hafnon

Hafnon
Very small brown single crystals of hafnon from Bernic Lake, Lac-du-Bonnet District, Manitoba, Canada
General
Category	Nesosilicates
Formula	HfSiO4
IMA symbol	Haf
Strunz classification	09.AD.30
Dana classification	51.05.02.02
Crystal system	Tetragonal
Crystal class	Ditetragonal Dipyramidal (4/mmm ) H-M symbol: (4/m 2/m 2/m)
Space group	I41/amd
Unit cell	a = 6.5725(7) Å, c = 5.9632(4) Å=; Z = 4
Identification
Colour	Orange-red, brownish yellow, rarely colourless
Crystal habit	Euhedral to irregular crystals
Cleavage	{???} Indistinct
Mohs scale hardness	7.5
Luster	Vitreous
Streak	grey white
Diaphaneity	Transparent
Density	6.97
Optical properties	Uniaxial (+)
Refractive index	nω = 1.930 - 1.970 nε = 1.980 - 2.030
Birefringence	δ = 0.050
Common impurities	Often zoned with zircon. Forms part of zircon-hafnon series

Hafnon is a hafnium nesosilicate mineral with the idealized chemical formula HfSiO₄. It is the mineral form of hafnium silicate and one of the few known minerals with essential hafnium.

Chemistry

Hafnon forms a solid-solution series with its zirconium counterpart, zircon (ZrSiO₄). Several other variants exist, with compositions such as (Hf,Zr,Th,U,Y)SiO₄. In nature, part of zirconium is replaced by the chemically similar hafnium, so natural zircon is never pure ZrSiO₄. However, a zircon with 100% hafnium substitution can be synthesized and is known as hafnon.

Hafnon occurs as transparent red to red-orange tetragonal crystals, with a Moh's hardness of 7.5.

Hafnon occurs naturally in tantalum-bearing granite pegmatites in Zambezia (Mozambique), and in weathered pegmatites at Mount Holland, Western Australia. It has also been reported at locations in Ontario, Quebec, and Manitoba, Canada; North Carolina, United States, and Zimbabwe.

References

• Emsley, John. Nature's Building Blocks. Oxford, 2001. ISBN 0-19-850341-5
• J. A. Speer, B. J. Cooper (1982). "Crystal structure of synthetic hafnon, HfSiO₄, comparison with zircon and the actinide orthosilicates" (PDF). American Mineralogist. 67: 804–808.

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