www.GemstoneBasics.com

Photomicrography > Peridot
First draft: November 12^th, 2016 | Last update: November 12^th, 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.

References and items of related interest

Furuya, M. & Davies, S. (2015). Gemological features of pallasitic peridot of six different meteorites In: Proceedings: 34^th 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. 3^rd edition. ABC Edition, Zürich, Switzerland, 234 p. ISBN 3-85504-030-3.
Note: 1^st 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. 3^rd 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: 32^nd International Gemmological Conference 2011, Abstracts, pp. 110-113. Search the Meteoritical Bulletin Database

Peretti, A. & Gübelin, E.J. (1996). New Inclusions in Pakistani Peridot: Vonsenite-Ludwigite Needles. JewelSiam, Vol. 6, No. 6 (December/January), pp. 68-69. Also published on www.gemresearch.ch

More peridot references

Terrestrial peridot

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

Peridot's birefringence of 0.036 to 0.038 is significant enough to influence results...
30x (FoV 3.30mm) X-Pol

... and thus a polarising filter is required to get acceptable photomicrographs
30x (FoV 3.30mm) X-Pol

This lilypad and (possibly) chromian spinel are diagnostic for peridot
50x (FoV 1.48mm) X-Pol

Double disc lilypad inclusion in a 2.82ct Pakistani peridot
50x (FoV 2.10mm; DoF 0.09mm) X-Pol

50x (FoV 2.22mm; DoF 0.06mm) Obl, Pol

50x (FoV 2.20mm; DoF 0.14mm) Obl, Pol

40x (FoV 2.30mm; DoF 0.62mm) Obl, Pol

Opaque euhedral inclusions with tension haloes are common in peridot
50x (FoV 1.48mm; DoF 0.38mm) Obl, Pol

Ludwigite-vonsenite needles in a 3.17ct peridot from Sapat Gali, Naran, Khagan Valley, Pakistan
18x (FoV 5.32mm; DoF 0.93mm) Obl, TL, Pol

Home

Back to top of page