Pectolite

pectolite

stevensite

wollastonite

basaltic cavities

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Formula: NaCa₂Si₃O₈(OH)
Inosilicate (chain silicate), single width, wollastonite group
Crystal System: Triclinic
Specific gravity: 2.84 to 2.9 meaasured, 2.87 calculated
Hardness: 4½ to 5
Streak: White
Colour: White, grey, sometimes greenish, yellowish, colourless
Solubility: Slightly soluble in hydrochloric acid
Environments:

Plutonic igneous environments
Basaltic cavities

Pectolite is a secondary mineral similar in occurrence to zeolites. It is found lining cavities in basalt, associated with zeolites, prehnite and calcite.

Localities

At the Cowgreen Dam quarry, Forest and Frith, County Durham, England, UK, veins were exposed composed of pectolite, with lenses of calcite, forming radiating crystalline bands parallel to the vein walls, and clusters of radiating crystals up to 10 mm across were found coating joints in dolerite (JRS 21.9-11).

At Force Garth Quarry, Forest and Frith, County Durham, England, UK, stevensite pseudomorphs after pectolite have been found (JRS 21.9-11).

At High Force Quarry, Forest and Frith, County Durham, England, UK, pectolite typically occurs as thin coatings of aggregates of radiating crystals, up to 100 mm across, coating joint surfaces. Stevensite pseudomorphs after pectolite have also been found here (JRS 21.9-11).

At Middleton-in-Teesdale, County Durham, England, UK, discontinuous veins of pectolite are comparatively common in the abandoned quarries, and stevensite pseudomorphs after pectolite have also been found here (JRS 21.9-11).

At Copthill Quarry, Stanhope, County Durham, England, UK, pectolite occurs as fine specimens of radiating joint coatings. Pseudomorphs of both calcite and quartz after pectolite have been found here (JRS 21.9-11, SY p164).

At Cambokeels Mine, Westgate, Stanhope, County Durham, England, UK, pectolite has been found as radiating coatings on dolerite from the same part of the workings that yielded analcime and apophyllite (JRS 21.9-11).

At Barrasford Quarry, Chollerton, Northumberland, England, UK, stevensite pseudomorphs after pectolite have been found (JRS 21.9-11).

At the Clee Hill quarry, Titterstone Clee Hill, Shropshire, England, UK, pectolite has been found on dolerite (RES p296).

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