Photomicrography > Peridot
First draft: November 12th, 2016 | Last update: November 12th, 2016
Some Features Observed in Peridot
Peridot is the gem variety of the mineral olivine which in fact encompasses a solid solution series between magnesium-rich end-member forsterite, Mg2SiO4, and iron-rich end-member fayalite, Fe2SiO4. With an average MgO value around 48wt% and FeO around 9wt%, peridot leans towards forsterite.
Identifying peridot is quite straightforward. If the tell-tale lilypad inclusions are not present, then at least peridot's typical yellowish-green colour in conjunction with its eye-visible birefringence provide important clues. Such high a birefringence always requires a polarising filter during photomicrography.
Besides the archetypal lilypads, crystal grains originating from Fe-Al assemblages (including substituting elements) are also likely to occur. These inclusions are typical of terrestrial peridot and are completely different from those found in the much rarer extraterrestrial peridots from pallasitic meteorites.
Furuya, M. & Davies, S. (2015). Gemological features of pallasitic peridot of six different meteorites In: Proceedings: 34th International Gemmological Conference IGC, Vilnius, Lithuania, 26-30 August 2015, pp. 85-88. The entire publication is available on www.igc-gemmology.net
Gübelin, E.J. (1983).
"Lotus Leaves" in Peridot In: Internal World of Gemstones. Documents from Space and Time, pp. 168-169.
3rd edition. ABC Edition, Zürich, Switzerland, 234 p. ISBN 3-85504-030-3.
Note: 1st Edition (1973). Innenwelt der Edelsteine. Urkunde aus Raum und Zeit. ABC Edition, Zürich, Switzerland, 233 p. ISBN 3-85504-030-3 (in German; ISBN checked in the original copies).
Gübelin, E.J. & Koivula, J.I. (1997). Peridot and its Inclusions In: Photoatlas of Inclusions in Gemstones, pp. 305-308. 3rd revised edition. ABC Edition, Zürich, Switzerland, 532 p., ISBN 3-85504-095-8.
Gübelin E.J. & Koivula J.I. (2005). Inclusions in Gems of Commercial Importance: Peridot In: Photoatlas of Inclusions in Gemstones. Volume 2, pp. 511-540. Opinio Publishers, Basel, Switzerland, 829 p., ISBN 3-03999-029-2.
Jan, M.Q. & Khan, M.A. (1996). Petrology of gem peridot from Sapat mafic-ultramafic complex, Kohistan, NW Himalaya. Geological Bulletin of the University of Peshawar, Vol. 29, pp. 17-26.
Kausar, A.B. & Khan, T. (1996). Peridot mineralization in the Sapat ultramafic sequence, Naran-Kohistan, Pakistan. Geologica, Vol. 2, pp. 69-75.
Koivula, J.I., Stockton, C. & Fryer C. (1980). Gemmological Notes: Diopside as an inclusion in peridot. Gems & Gemology, Vol. 16, No. 9 (Summer), pp. 332-333.
Koivula, J.I. (1995). Ludwigite in peridot. Lapidary Journal, Vol. 49, No. 2, p. 16.
Leelawathanasuk, T., Atichat, W., Suthirat, C., Wathanakul, P., Sriprasert, B., Naruedeesombat, N., Srithunayothin, P. & Davies, S. (2011). Pallasitic peridot: The gemstone from outer space. Proceedings: 32nd International Gemmological Conference 2011, Abstracts, pp. 110-113. Search the Meteoritical Bulletin Database
Legend: FoV: Field-of-View; DoF: Total focusing depth; DF: darkfield; Obl: oblique illumination (fiber optics); Pol: polarising filter before objective; Sh: shadowing; Refl: reflected light; TM: transmitted illumination, UVL: long-wave ultra-violet radiation; UVS: short-wave ultra-violet radiation; X-Pol: crossed polarising filters