- Chemistry: Na2Zr(SiO3)3 - 3H2O , Hydrated Sodium Zirconium Silicate.
- Class: Silicates
- Subclass: Cyclosilicates
- Uses: Only as mineral specimens.
Hilairite is one of the many new minerals to come from the famous mineral locality, Mont Saint-Hilaire, Quebec, Canada.
Hilairite's crystals are small but generally well formed and they have an interesting brown color and a good luster.
Its rarity and beauty as well as its ties to this wonderful site make this a great collection mineral if a specimen can be found.
The rocks at Mont Saint-Hilaire are unique because they are the result of an alkaline metal rich intrusion called an agpaitic pegmatite.
This pegmatite was also rich in traditionally rarer elements such as titanium, zirconium, cerium, barium and others.
Hilairite is certainly one of the minerals that typify this pegmatite having sodium (one of the alkali metals) and zirconium in its chemistry.
In fact there are several different minerals that are sodium zirconium silicates that are associated to hilairite.
These include the closely related gaidonnayite whose formula, Na2Zr(SiO3)3 - 2H2O only differs in the number of water molecules.
Catapleiite is a dimorph of gaidonnayite, having the same chemistry but different structures.
The mineral elpidite has a formula of Na2ZrSi6O15 - 3H2O and differs only in the amount and ratio of silica.
Of course the structure may be very different.
- Color is bronze yellow or dark brown to pink.
- Luster is vitreous to waxy.
- Transparency: crystals are transparent to translucent and opaque.
- Crystal System is trigonal; bar 3 2/m
- Crystal Habits include small prismatic (three or six sided) crystals with rhombohedral terminations.
Twinning is common and crystals are found doubly terminated.
- Cleavage is not observed.
- Fracture is conchoidal.
- Hardness is 4 or better.
- Specific Gravity is 2.72 - 2.74 (average)
- Streak is white.
- Associated Minerals are gaidonnayite,
- Notable Occurrence is limited to Mont Saint-Hilaire, Quebec, Canada.
- Best Field Indicators: crystal habit, color, luster and