In fact there are several different minerals that are sodium zirconium silicates that are associated to hilairite. 2 O 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 Na 2 ZrSi 6 O 15 - 3H 2 O 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. Twinning is common and crystals are found doubly terminated. Cleavage is not observed. Fracture is conchoidal. Hardness is 4 or better.