Catalog Search Guide
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Gyrolite
Gyrolite is a rare hydrated calcium silicate mineral, formula NaCa16Si23AlO60(OH)8·14H2O, belonging to the phyllosilicate class and classified within the broader gyrolite group alongside related species such as tungusite and centrallasite. It typically forms as radiating, spherical or nodular aggregates in a pseudohexagonal habit, with colors ranging from colorless and white to pale brown or green, a vitreous luster, perfect cleavage, and a Mohs hardness of only 2.5. Its very name, from the Greek word for "circle," reflects this signature globular growth habit, which develops when silica-rich hydrothermal fluids interact with calcium-rich volcanic rock at relatively low temperature, filling vesicles, amygdules, and veinlets in altered basalts and tuffs.
The type locality is The Storr, near Portree on the Isle of Skye, Scotland, where the species was first described in 1851; nearby occurrences at 'S Airde Beinn on the Isle of Mull and at Ballintoy and Ballhenry in County Antrim, Ireland, are equally classic for the region's basalt-hosted zeolite suites. Exceptional and highly sought specimens come from the Deccan Trap basalt quarries around Mumbai, India — particularly Malad Quarry and Dindoshi in Maharashtra — where gyrolite forms lustrous spherules in association with okenite, apophyllite, prehnite, stilbite, and other zeolite minerals. Other notable finds include the basalts of the Faroe Islands and Greenland, the classic Crestmore Quarries in California, and Italian occurrences at Elba and Monte Biaena in Trentino-Alto Adige; gyrolite has also been reported from Australia, Canada, China, the Czech Republic, Iceland, and Japan.
Collectors prize gyrolite for its delicate, almost porcelain-like spherical crystal habit and its role as a defining accessory mineral in composite basalt-cavity specimens alongside apophyllite, prehnite, and zeolites. Because well-formed, aesthetic examples are uncommon outside a handful of classic basalt terranes, fine gyrolite specimens — especially the glassy Indian nodules and Skye type-locality material — remain a distinctive addition to any systematic silicate or zeolite-association collection.
