|I purchased this stone while uncut, in May 2000 while staying in Ratnapura, Sri Lanka. It was said to came from the Kolonne area, of Sri Lanka. The sellers thought it might be serendibite, which can occur in a similar colour and is known to come from the Kolonne area. (1)
It had strong trichroism evident with the dichroiscope, the colours were: blue, green and colourless.
The OPL prism hand spectoscope revealed a fine line in the blue, looking similar to the spectum below.
|A spot R.I. with the refractometer was approximately 1.62.
The only possibility that came to mind was a rare blue andalusite. Such an andalusite from Belgium had been described in the literature (2).
Andalusite is trichroic and is also known to sometimes have lines in the blue section of the VIS spectrum.(3)
I bought the piece and sent it to the cutter.
After a full refractive index was determined, 1.58-1.620 BR 0.039 and the specific gravity of 2.96 was obtained, a review of the literature led me to conclude that it might be the mineral grandidierite.(4)
Grandidierite had never been reported from Sri Lanka, but It had been found in a few localities in Madagascar. The Madagascar material was said never to be totally transparent, only at best translucent.(4)
I decided to contact Dr. Karl Schmetzer in Germany as this stone needed advanced testing.
This turned into a detailed paper that was published in Gems & Gemology, Spring 2003 Vol. 39 No.1 page 32-37, Titled: The First transparent Faceted Grandidierite, From Sri Lanka by Karl Schmetzer, Murray Burford, Lore Kiefert, and Heinz-Jürgen Bernhardt
|An interesting paper (6) describes how Sri Lanka and Madagascar were once, hundreds of millions of years ago, part of the continent called Gondwana.
According to a map with the paper the Kolonne area of Sri Lanka, and the location in South Eastern Madagascar where grandidierite was first discovered in 1902, (Cape Andrahomana, Taolagnaro, formally called Fort Dauphin) were once approx. 60 km apart.
I have since sold the grandidierite to a Swiss collector, the late Dr. E. Gübelin who has a very large collection of rare Sri Lankan gemstones.
(1) Serendibite from Sri Lanka by K. Schmetzer, G. Bosshart, H. J. Bernhardt, E. .J. Gübelin, C. Smith
(2) Blue andalusite from Ottre, Venn-Stavelot Massif, Belgium Bulletin de Mineralogie Vol. 107, 1984
(3) The Spectroscope and Gemmology by Anderson & Payne 1998 pg. 210-213
(4) Color Encylcopedia of Gemstones by Joel Arem 1977 pg.58-59
(5) The First transparent Faceted Grandidierite, From Sri Lanka by Karl Schmetzer, Murray Burford, Lore Kiefert, and Heinz-Jürgen Bernhardt Gems & Gemology Vol. 39 No. 1 Spring 2003 pg. 32-37.
(6) Sri Lanka-Madagascar Gondwana Linkage: Evidence for a Pan-African Mineral Belt by C.B Dissanyake and Rohana Chandrajith The Journal of Geology V 197, pg. 223-235 1999