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: Ca2Mg4.5Al1.5Si3.6Al1.8B0.6O20
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.
Comparism-of-the-properties-of-zoisite(tanzanite),Serendibite and sapphirine
Figure1
- First-faceted-serendibites-in-gemmological-literature
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
- Faceted Serendibite Gemstone
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.
The Second Faceted Serendibite
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.
No related posts.