Colourless Diopside from Kenya and Canada
first published in Facette 22 (February 2016) Diopside, a calcium magnesium clinopyroxene (MgCaSi2O6), an end-member of the diopside-hedenbergite series (pyroxene) is a rather rare gem species in the trade. Commonly found in greenish brown stones (mostly due to iron content) to dark brown cabochons with an obl
Zircon Showing Asterism
first published in Facette 22 (February 2016) Martin Steinbach, a collector of star stones from Idar-Oberstein (Germany), submitted to the SSEF a zircon with a star effect (asterism), which – to the knowledge of the author – so far had not been described in literature for this gem. The zircon speci
by Dr. M.S. Krzemnicki, first published in Facette 20 (January 2013) After studying and describing colour-changing bastnäsite in the 2012 Facette (Herzog 2011 & Herzog 2012), we have this year focussed research on colour-changing zircon from Burma in collaboration with Mr. O. Waldis, who kindly lent us a
The Usambara Effect and other colour-change Effects in Gemstones
Colour change in gemstones is an interesting phenomenon, which can be due to a number of reasons. One of the causes is the so called Usambara effect, a type of colour change which is not so well known in the public. In contrast to the alexandrite effect, this phenomenon is not dependent on the type of illuminat
The Beryl Group – an Overview
The Beryl Group – an Overview. Published in Journal of the Gemmological Association of Hong Kong GAHK, 2020, Volume XLI, 48-54.
Purple Mozambique Garnet
In early 2016, attractive bright purple garnets arrived at SSEF in Bangkok, Basel and Hong Kong. Based on client information, they are from a new mine, Padagaga in the Chimoio area in Mozambique, which was discovered recently.
Grandidierite and other Rare Gemstones at SSEF
We would like to present three minerals which were tested in the past few months at SSEF and which at least partially made headlines in the news for collectors and aficionados of such gemmological rarities.
Exceptional Spessartine Garnets
first published in Facette 21 (February 2014) In 2013, the SSEF tested a number of very outstanding spessartine garnets. This manganese dominated member of the garnet group commonly shows a highly attractive and vivid orange colour and is thus also known and described in the trade as ‘Mandarin garnet
Exceptional Colour Change Garnets Showing the Usambara Effect
by Dr. M.S. Krzemnicki, first published in Facette 21 (February 2014) Colour change, also known as“alexandrite effect” has been studied extensively since it was first described in 1831 for alexandrite (chromium-bearing variety of chrysoberyl) from Russia (von Pott, 1842). Since then, numerous minerals or g
Gemstones of the Garnet Group – about mixed crystals and solid solution
Gemstones of the Garnet Group – about mixed crystals and solid solution. Published in Journal of the Gemmological Association of Hong Kong GAHK, 2019, Volume XL, 36-49.