Discovery of a new stone Serendibite – Gem Quality

By Dunil Palitha Gunasekara, Dip. Gem. FGA

President: Crystals Gallery -Gem Lab No 28 Batugedera , Ratnapura, Sri Lanka

This article is reproduced with kind permission from the National Gem and Jewellery Authority

Abstract

A Bluish- Green colour, emerald cut gemstone , weighing 0.35 carat and measuring 4.42 X 3.80X 2.80mm has been identified as a serendibite of gem quality by the GIA laboratory , Santa Monica , California, USA on date 08 January 1997. Identification report no: 10035658 and is the first faceted serendibite recorded in the gemmological literature

These gems may be confused with sapphire and zoisite but can be identified as serendibite on the basis of refractive indices , twinning, and spectroscopic features . Serendibite derived from the old Arab name for Ceylon -Now Sri Lanka – in recognition of this country as the type locality for this mineral . The first description of the mineral  serendibite was published in 1903 by Prior and Coomaraswamy for the Boron bearing Ca-Mg-Al -silicate that was discovered in a contact zone between granulite limestone at Gangapitiya , near Ambakotte ,Kandy, Sri Lanka.

Serendibite

Chemical Formula:Ca2(Mg,Al)6(Si,Al,B)6O20

Emperical Formula: Ca₂Mg_4.5Al_1.5Si_3.6Al_1.8B_0.6O₂₀

Group: Aenigmatite

Crystal System: Triclinic

Occurrence: Associated with sapphirine, feldspar ,mineral vein

Locality: Ginigalgoda ,Kolonne, Sri Lanka

Appearance and Physical Properties

Habit: as rolled pebbles .

Colour: bluish-green

Lustre: vitreous

Fluorescence: LW & SW Inert

Hardness 7

Clarity: Transparent.

Specific Gravity: 3.44

Optical Properties

Refractive Indices:

alpha-1.697

beta-1.700

gamma-1.702

Birefrigence: 0.005

Optic character: biaxial negative

Absorption spectrum: a weak line at 470 nm.

Microscopic features: Polysynthetic twinning , white-mineral inclusions

Pleochroism: Strong Green/yellow/blue

Identification

Serendibite gem quality first RI reading alpha is 1.697.Sapphirine is 1.700 and Zoisite is 1.692.

Figure1

These two stones , both from Sri Lanka , are the first faceted serendibites recorded in the gemmological literature . The sample on the left weighs 0.35 carats and the one on the right weighs 0.55 carats.

Figure 2

Both faceted serendibites showed evidence of twinning  at 20X magnification , the 0.55 carat sample reveals two polysynthetically twinned areas within untwinned regions Immersion ,crossed polarizers.

Figure3

The second faceted serendibite 0.55 carat . Measurements: 4.98X 4.95 X2.72 mm.

Discoverer of the Serendibite- Gem Quality : Dunil Palitha Gunasekera, Gemmologist ,Ratnapura, Sri Lanka.

References

Prior G. T., Coomaraswamy.A.K, 1903 Serendibite , a new borosilicate from Ceylon . Mineralogical Magazine , Vol 13 , No 61 pp 224 to 227.

Reinitz .I., Johnson.M.L, 1997 Gem Trade Lab Notes : Serendibite ,a rare gemstone. Gems and Gemmology vol 33., No2 pp 140 -141.

Schmetzer K, Bosshart. G., Bernhardt.H.J., Gubelin .E.J., Smith. C.P, (2002). Serendibite from Sri Lanka , Gems and Gemmology volume 38, No 1 ,pp 73-79.