Formula:Na2ZrSi3O9.3H2O
Cyclosilicate, hilairite group
Crystal System: Trigonal
Specific gravity: 2.724 measured, 2.739 calculated
Hardness: 4½
Streak: White
Colour: Pale to dark brown, white, yellow, colourless, flesh-pink, rose-red
Solubility: Slightly soluble in hydrochloric and nitric acids, but not by sulphuric acid
Common impurities: Ti,Al,Fe,Mn,Mg,Ca,K
Environments
Hilairite is a rare zirconium-bearing mineral.
Localities
At the type locality, the Poudrette quarry, Mont Saint-Hilaire, La Vallée-du-Richelieu RCM, Montérégie, Quebec, Canada, hilairite
occurs as 0.1 to 1.0 mm crystals and more commonly as aggregates in miarolitic cavities and altered pegmatite dikes in
nepheline syenite.
The crystals are found on analcime, microcline,
or natrolite, usually associated with calcite,
aegirine, albite,
catapleiite and gaidonnayite.
They are often coated with a veneer of chlorite. Other associated minerals include
elpidite, epididymite,
fluorite, pyrite,
sphalerite, aegirine and
galena
(CM 12.237-240, HOM, Dana).
At Langesundfjord, Norway, hilairite occurs in hydrothermally altered pegmatites
(Dana).
Alteration
On heating hilairite loses all of its water at 220oC and at least 95% of the original water is recovered on
cooling from 855oC to room temperature
(CM 12.237-240).
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