Prehnite Pseudomorph of laumontite and gyrolite Locality: Malad , Ward 38, Mumbai (Bombay) , Mumbai District (Bombay District), Maharashtra , India size : 21x15cm) — Photo: Didier Descouens · CC BY-SA 4.0
Gyrolite
A rare hydrated sodium-calcium sheet silicate — the 'N-C-S-H' mineral of cement chemistry — forming white spherulites in basalt cavities.
Intro adapted from Wikipedia (CC BY-SA).
Gyrolite is an IMA-recognized mineral species in the silicate class, with the chemical formula NaCa₁₆(Si₂₃Al)O₆₀(OH)₈·14H₂O.
It crystallizes in the triclinic crystal system (space group P-1). It is a member of the Gyrolite structural group.
Key properties: Mohs hardness 3–4; specific gravity 2.39; Vitreous to pearly luster; optically uniaxial.
IMA symbol Gyr, grandfathered status — known before the IMA’s founding, named in 1851.
Occurs as replacements of wall rocks and in vugs, amygdules, and veinlets in basalts; in hydrothermally altered rhyolites and sediments; in some ore deposits.
It is found associated with Apophyllite, stilbite, laumontite, thomsonite, okenite, tobermorite, xonotlite, calcite.
Its name comes from the Greek for round, in reference to its common habit.