Feruvite

Images

Formula: CaFe²⁺₃(Al₅Mg)(Si₆O₁₈)(BO₃)₃(OH)₃(OH)
Cyclosilicate (ring silicate), tourmaline group
Crystal System: Trigonal
Specific gravity: 3.207 measured, 3.21 calculated
Hardness: 7
Streak: Grey
Colour: Dark brownish black
Common impurities: Ti,Mn,K,Na
Environments

Pegmatites
Hydrothermal environments

Feruvite occurs in hydrothermally altered pegmatitic quartz veins (Webmin).

Localities

At the Sullivan Mine, Kimberley, Fort Steele Mining Division, British Columbia, Canada, feruvite has been discovered in the footwall of the lead-zinc-silver deposit near gabbro sills and dikes. The most important factor controlling feruvite formation is likely the reaction of iron-rich hydrothermal liquids with calcium-rich minerals in gabbro and host rocks. This reaction led to the breakdown of calcium-rich minerals, plagioclase and hornblende, with release of calcium to solution and its incorporation into feruvite. This process probably post-dated the main stages of formation of fine grained intermediate schorl-dravite in the tourmaline pipe in the footwall, and is attributed to intrusion of gabbro and associated albite-chlorite-pyrite alteration (CM 34.733-740).

At the Red Cross Lake pegmatites, Red Cross Lake, Manitoba, Canada, feruvite occurs in the calcium-rich contacts of lepidolite-bearing granitic pegmatites where the pegmatites intrude metamorphically altered andesite and basalt host-rocks. In addition to tourmaline, the contacts contain cesium and rubidium rich biotite, iron-rich muscovite, epidote, apatite, calcium-rich garnet, titanite, calcite, quartz and arsenopyrite.
The tourmaline is commonly zoned, with a core of feruvite surrounded by schorl or dravite, and rimmed by uvite. In plane-polarized light, uvite and dravite are mainly pale blue or blue, and feruvite and schorl are mainly dark blue. Brown schorl and feruvite tend to be rich in titanium. The wallrocks provided the iron and calcium for contact-metasomatic reactions between the wallrocks and the intruding pegmatite to produce feruvite (CM 36.433-439).

At the type locality, Repanga Island (Cuvier Island), Thames-Coromandel District, Waikato Region, New Zealand, feruvite occurs in a pegmatitic, tourmalinised rock whose origin has been attributed to hydrothermal replacement of the aluminous and ferromagnesian host-rock silicates by tourmaline and tourmaline-quartz vein sequences. The feruvite occurs as feruvite/dravite cores surrounded by schorl/dravite. Associated minerals include quartz, microcline, chlorapatite and pyrite (CM 27.199-203).

Back to Minerals