Surinamite

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Formula: Mg₃Al₃O(Si₃BeAlO₁₅)
Inosilicate (chain silicate), sapphirine supergroup, beryllium-bearing mineral
Crystal System: Monoclinic
Specific gravity: 3.3 measured, 3.58 calculated
Streak: White
Colour: Blue-green, dark blue
Common impurities: Ti,Mn,Zn,Ca,F
Environments

Pegmatites
Metamorphic environments

Surinamite occurs in regional metamorphic environments, in most cases formed by alteration of beryllium-bearing cordierite (Dana).

Localities

At Casey Bay, Napier Complex, Enderby Land, Eastern Antarctica, surinamite occurs in sillimanite-rich segregations in pegmatites, associated with quartz, sillimanite, sapphirine and taaffeite (HOM).

At the type locality, the Bakhuis Mts, Sipaliwini District, Suriname, surinamite was found in a mylonitic mesoperthite gneiss, with about equal amounts of medium-grained mesoperthite and quartz, and some oligoclase. This gneiss was probably formed during high-pressure granulite facies metamorphism of aluminous rocks. Minor constituents are green biotite, kyanite, sillimanite, surinamite and green spinel. Accessories include opaque minerals, zircon, and small rutile needles. Sillimanite is present in three generations:
(1) rather large individual crystals
(2) small crystals in aggregates together with biotite, kyanite and surinamite
(3) in very fine-grained fibrolite along shear zones
Surinamite, in small crystals of up to 0.2 mm in size, is found only in aggregates together with biotite, kyanite and sillimanite. Locally, intergrowths have been found between kyanite and surinamite and between sillimanite and surinamite (AM 61.193-199.

At the Surinamite-bearing gneiss locality, Harris, Isle of Lewis and Harris, Outer Hebrides, Scotland, UK, surinamite occurs as tiny grains enclosed in kyanite or as tabular grains up to 1 mm long mostly surrounded by silicon-rich cordierite. A few surinamite grains enclose orthopyroxene, sillimanite, and silicon-rich sapphirine.
It is suggested that surinamite formed at first by the continuous reaction:
BeSiAl_–2 (in sapphirine) + sillimanite + orthopyroxene → surinamite + quartz
and, subsequently, by the discontinuous reaction:
beryllium-depleted sapphirine + quartz → surinamite + orthopyroxene + kyanite
with increase of pressure to >12 kbar at 850–900 °C.
During subsequent decrease in pressure and temperature:
surinamite + orthopyroxene + kyanite + quartz → beryllium-rich cordierite (AM 85.1474-1484).

At Chimwala, Chipata District, Eastern Province, Zambia, surinamite occurs as pseudomorphs after cordierite (HOM).

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