Gaidonnayite (Type Locality)
(Na,K)₂ZrSi₃O₉ · 2H₂O

     Mont Saint-Hilaire is the type locality for gaidonnayite. It was originally found in 1967, however, there was not enough material to describe its chemistry and it was assigned UK #27. In the summer of 1972, more than a hundred small crystals were found on a natrolite specimen and much of the previous work was repeated with the new material.

     It is the orthorhombic dimorph of catapleiite. Some crystals are found with a very fine coating of a chlorite-like mineral, causing a grayish or greenish color.

PHYSICAL CHARACTERISTICS:

Color ranges from pale yellow, very pale brown, pale gray and
   gray-green to colorless.
Luster is adamantine to vitreous.
Diaphaneity is usually transparent, occasionally translucent to opaque.
Crystal System is orthorhombic; P2₁nb.
Crystal Habits include equant, blocky, tabular and wedge-shaped
   crystals; stacked spherical groups and druses.
Cleavage: none observed.
Fracture is conchoidal.
Hardness is 5
Specific Gravity is approximately 2.7g/cm³.
Streak is white.
Associated Minerals include aegirine, albite, amphibole group,
   ancylite, burbankite, calcite, catapleiite, chlorite group, elpidite,
   epididymite, eudialyte, fluorite, galena, goethite, hilairite, microcline,
   natrolite, pyrite, pyrochlore, rhodochrosite, sérandite, siderite,
   sphalerite and zircon.
Distinguishing Features: Crystal habit. Fluoresces bright green under
   SW and LW (there exists a non-fluorescent variety of gaidonnayite).
Origin: Named in 1974 for Gabrielle Hamburger Donnay (1920-1987),
    crystallographer and mineralogist, McGill University, Montréal, Canada.

CLASSIFICATION:

REFERENCES:
CanMin 12:316-319 (1974), CanMin 23:11-15 (1985),
MinRec 21:310-311 (1990), Dana 8:1227-1228 (1997)

DISTRIBUTION AND RARITY AT MONT SAINT-HILAIRE:

Legend