Stellerite

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Formula: Ca₄(Si₂₈Al₈)O₇₂.28H₂O
Tectosilicate, zeolite, stilbite subgroup
Crystal System: Orthorhombic
Specific gravity: 2.13 measured, 2.12 calculated
Hardness: 4½
Streak: White
Colour: Colourless to white, pink, orange
Solubility:
Common impurities: Fe,Mn,Mg,Sr,Ba,Na,K
Environments

Pegmatites
Hydrothermal environments
Basaltic cavities

The most attractive crystals of stellerite are found in cavities in basalt, but stellerite is also found in hydrothermal systems in a wide variety of host rocks, such as hornfels, granites, granitic gneiss, pegmatites and amphibolites, and in geothermal fields (Mindat, Dana). Associated minerals include other zeolites, prehnite, apophyllite and tridymite (HOM, Dana).

Localities

At the Hunter Valley, near Allandale, Northumberland county, New South Wales, Australia, stellerite occurs in andesite as groups of crystals to 6 mm associated with earlier datolite (AJM 18.2.35).

At Garrawilla Station, Pottinger county, New South Wales, Australia, exceptional specimens of pale pink, bright salmon-orange, red or brown stellerite are commonly associated with deep red heulandite and are covered by drusy quartz aggregates, calcite, analcime, laumontite, and, very rarely, with natrolite, in veins and cavities, up to 1.5 metres in diameter, in highly weathered, porous, olivine basalt and trachyte (ZW).

At the Lake Cooper quarry, Corop, Campaspe Shire, Victoria, Australia, stellerite occurs, in veins cutting metadolerite as colourless bladed crystals to 2 mm long accompanying axinite-(Fe), as drusy crystals on joint planes, and in small cavities in quartz veins (AJM 11.1.30).

At the Dookie Mineralogical Reserve quarry, Dookie, City of Greater Shepparton, Victoria, Australia, colourless stellerite crystalS, up to 0.5 mm long, are found in metavolcanics and dolerite (ZW).

At the The Harcourt Quarries, Harcourt North, Mount Alexander Shire, Victoria, Australia, colourless to pale pink flat-topped blades of stellerite are associated with babingtonite, titanite, fluorapophyllite and calcite in miarolytic cavities in granite (ZW).

In the Aurangabad District, Maharashtra, India, exceptional specimens of colourless to pale orange, transparent stellerite crystals form rows and aggregates of flat-topped crystals (with tiny triangular modifications), up to 10 cm in diameter, on a mat of white mordenite needles (up to 2 cm thick) and deep red heulandite in large cavities in basalt near Aurangabad (ZW).

At Syed Pimpri, Nashik District, Nashik Division, Maharashtra, India, colourless, flat-topped stellerite crystals up to 1 cm long, and pointed, pink stilbite blades occur on quartz in basalt (ZW).
At Nasik stellerite usually crystallises on quartz, but also frequently on laumontite (Minrec 34.1.62).

Near Chakan, Pune District, Pune Division, Maharashtra, India, spherical aggregates of stellerite associated with heulandite and okenite are found in cavities in basalt (Minrec 34.1.62).

At the type locality, Mednyi Island, Commander Islands, Bering Sea, Kamchatka Krai, Russia, stellerite was first described from sea cliffs of brecciated dolerite tuff along the northwest cape of Copper Island. The crystals are light pink, pointed laths, up to 5 mm long, lining the walls of veins, up to 3 cm thick, and are commonly covered with native copper and calcite. Nearby cavities contain analcime and quartz. Stellerite is reported with laumontite, stilbite, heulandite and mordenite in cavities at 190 to 220^oC in the geothermal field at Paratumskoe.
Stellerite is found with chabazite and heulandite on gneiss at Mount Medvezhyi (ZW).

At Malmberget, Gällivare, Norrbotten County, Sweden, golden to brown, flat-topped stellerite forms radial spheres, up to 15 mm across, on biotite and feldspar (ZW).

At Dunseverick, Giant's Causeway, Co. Antrim, Northern Ireland, UK, both stilbite and stellerite are found in the same cavities (ZW).

At Craigahulliar Quarry, Portrush, County Antrim, Northern Ireland, UK, flat-topped stellerite occurs (ZW).

At Tardree Mountain, County Antrim, Northern Ireland, UK, flat-topped, rectangular crystals of stellerite, only 1mm long, are found in rhyolite (ZW).

At Granite Creek Basin, west of Juneau , Alaska, USA, flattened, hemispherical aggregates of stellerite, composed of crystals up to 2.5 mm long, are found on fault surfaces cutting mineralised mica schist between masses of diorite (ZW).

At an unnamed Zeolite occurrence, South Fork San Onofre Canyon, San Clemente area, San Diego county, California, USA, stellerite is reported in veins in the contact zone of a quartz latite stock and the country rock (ZW).

At Berlin, Worcester county, Massachusetts, USA, grey, spherical aggregates of stellerite, up to 1cm in diametcr, are associated with heulandite on chlorite schist (ZW).

At Fanwood Quarry, Watchung, Somerset county, New Jersey, USA, excellent specimens of beige-brown, yellow, orange, or white, radiating fans and smooth hemispheres of stellerite, up to 3 cm in diameter, are found on beige heulandite or golden calcite in cavities, up to 30 cm in diameter, in Jurassic (201.3 to 145 million years ago) vesicular basalt flows. Nearby cavities contain gmelinite, bornite, datolite, prehnite, albite, quartz, pectolite, chalcopyrite, and, rarely, anhydrite and glauberite casts (ZW).

At the Braen quarry large white to cream coloured spheres of stellerite up to 4 cm have been found on drusy stellerite in cavities in basalt (Minrec 40.6.520).

At Hook mountain, Rockland county, New York, USA, light yellOW, spherical aggregates of stellerite, up to 1 cm in diameter, are reported with heulandite on basalt (ZW).

At the Dyer Quarry, Gickerville, Birdsboro, Berks county, Pennsylvania, USA, in a pocket in trap rock, specimens of stellerite to 60 cm across have been found. Microscopic heulandite and chabazite crystals are present on some specimens, but there are no other crystalline minerals (R&M 94.4.358-365).

At the Kibblehouse Quarry, Perkiomenville, Marlborough Township, Montgomery county, Pennsylvania, USA, stellerite is abundant in fracture fillings and pockets in the hornfels adjacent to dolerite, associated with chabazite and calcite. Temperature appears to be the controlling factor, with stellerite forming at lower temperatures than stilbite (R&M 94.4.358-365).

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