Serendibite

serendibite

uvite

warwickite

sinhalite

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Formula: Ca4[Mg6Al6]O4[Si6B3Al3O36]
Inosilicate (chain silicate), aenigmatite group, boron-bearing mineral
Specific gravity: 3.42 to 3.52
Hardness: 6½ to 7
Streak: White
Colour: Pale yellow, blue-green, greyish blue
Solubility: Only slightly attacked by acids
Common impurities: Ti,Fe,Mn,Na,K,F,H2O,P
Environments

Metamorphic environments

Serendibite occurs typically in contact metamorphosed calc-silicate rocks, particularly gneiss, in zoned metasomatic skarn between marble and feldsathic rock, tonalite or granulite. Typical associated minerals include diopside, apatite, calcite, clinopyroxene, spinel, pargasite, phlogopite and plagioclase, but quartz is conspicuously absent. Tourmaline, grandidierite and sinhalite may or may not be directly associated (Dana). Other associated minerals include scapolite, calcite, tremolite, microcline variety hyalophane, uvite, clinozoisite, forsterite, warwickite and graphite (HOM).

Localities

At Nunavut, Canada, serendibite occurs in skarn which formed between marble and granite on the Melville Peninsula, District of Franklin. The serendibite is associated with augite variety fassaite, uvite-rich tourmaline, clinozoisite, spinel and calcite. Comparison with other occurrences suggests that the stability field of serendibite may be restricted to silica-undersaturated bulk composition (CM 15: 108-112).

At the Portage-du-Fort area, Pontiac RCM, Outaouais, Quebec, Canada, serendibite crystals occur exclusively in a calc-silicate rock, and fine-grained serendibite occurs with aluminous diopside (CM 52:1-14).
Serendibite was discovered in a lens of boron-rich calc-silicate rock metamorphosed at 6–7 kbar, 650–700oC. The following stages of mineralisation are recognized:
(1) a prograde assemblage consisting of K-feldspar, tourmaline and calcite, inferred from relicts in scapolite
(2A) a peak metamorphic assemblage of aluminous diopside, serendibite, lesser phlogopite, and local scapolite
(2B) continued formation of phlogopite around serendibite in calcite pockets although serendibite was stable
(3) high-temperature breakdown of serendibite to uvite + spinel + calcite, and of aluminous diopside to pargasite.
The final stage is localised, low-temperature alteration to fine-grained phyllosilicates (CM 52: 595-615.).

At the Tayezhnoe Fe-B skarn, Aldan, Sakha Republic, Russia, the iron ore deposit contains the world's most extensive development of serendibite, found
(l) as grains, up to a few centimeters, in magnesian skarn with clinopyroxene, potassium pargasite, spinel, anorthite, uvite, phlogopite, and, locally, anhydrite
and
(2) as rare grains, 0.02-0.4 mm, in olivine-rich orthosilicate rock with clinohumite, potassium-rich pargasite, uvite, spinel, magnetite, ludwigite and sinhalite.
The sequence of mineral formation is
(l) formation of skarn containing spinel [1] + anorthite + clinopyroxene and plagioclase + clinopyroxene (local orthopyroxene) during upper amphibolite to granulite facies metamorphism (to 850oC, 4-5 kbar)
(2) introduction of boron to form ludwigite, serendibite and tourmaline (sodian uvite and uvite) at 600-700oC
(3) replacement of earlier formed serendibite to form uvite, calcite, spinel [2] and rare clintonite, and formation of serendibite + pargasite
(4) low-temperature alteration to chlorite, clinozoisite, grossular, margarite and aluminous uvite.

serendibite is a mineral characteristically found in silica-undersaturated skarn metamorphosed in the presence of H2O-rich fluids at relatively high temperatures (600-825oC) and low to intermediate pressures (less than l0 kbar) (AM 76.1061-1080).

At the type locality, Gangapitiya, Ambakotte, Kurunegala District, North Western Province, Sri Lanka, serendibite was discovered. Bands of granulite, which is composed mainly of quartz and feldspar, alternate with bands of limestone up to 18 inches wide. Between limestone and granulite occur contact zones consisting, next to the limestone, almost entirely of colourless diopside, but near the granulite the zones consist of a mixture of diopside with blue spinel, a little apatite, occasional scapolite or plagioclase, and serendipite (MM 13(6): 224-227)

At Johnsburg Township, Warren county, New York, USA, serendipite is associated with sinhalite (Dana).

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