Gyrolite, Ca2Si3O7(OH)2.H2 O, (Hydrated Calcium Silicate Hydroxide) forms cube-like aggregates. These are often fibrous but most famously glassy. Unlike similar looking minerals, such as Prehnite, Gyrolite usually forms individual formations as opposed to fused growths. The aggregates are often accompanied by many of the zeolites. Ryerite is a mineral closely related to Gyrolite. Both form inside volcanic vesicles when silica is in short supply.

Description: A thick matrix of blue-green Prehnite which is richly studded by rectangular blocks of Gyrolite. There is a particulalry large concentration of these at one end of the specimen, as well as on the underside. Here they can be particulalry well seen as they are not overgrown or obscured by the Prehnite. A very good specimen of a rare and unusual mineral.

Location: Malad Quarry, Mumbai, India.