Mesolite, Zeolite group of tectosilicates, formula Na₂Ca₂Al₆Si ₉O₃₀.8H₂O.

Crystal system: Orthorhombic (crystals long prismatic, commonly as hair-like tufts)
Hardness: 5
Density: 2.27
Colour: Colourless, white or grey (sometimes yellowish).
Streak: Colourless or white.

Mesolite is a member of the Zeolite group. Zeolites are tectosilicates having a large open crystal structure, containing water. Mesolite occurs with natrolite scolecite and other zeolites in cavities in volcanic rocks. Mesolite occurs in many localities but few yield fine crystal specimens. One locality renowned for its fine quality mineral specimens is the Poona, Maharashtra district of India.

This specimen of Mesolite comes from Ballynulto Quarry, Broughshane, County Antrim.