Mineral Sciences - Eloïse Gaillou | Natural History Museum of Los Angeles

Diamond Studies

By Eloïse Gaillou

About my research... and general information on diamonds.

I-THE COLOR OF DIAMONDS.

I-1. THE NATURE OF THE PINK COLOR IN NATURAL DIAMONDS.

I-2. BORON CONTENT IN NATURAL BLUE DIAMONDS.

I-3. DIAMONDS IN THE NATIONAL GEM COLLECTION.

II- THE ORIGIN OF DIAMONDS.

III- PUBLICATIONS.

I-THE COLOR OF DIAMONDS.

Fig. 1: Rose cut and cuboid rough diamonds, showing a variety of colors.

Diamonds don't only come in "white" (or properly speaking: colorless). Their color variety spans the full spectrum range: from brown (the most common color for diamonds), to black, to milky, to yellow, to the rarest green, orange, pink, purple, red and blue (see Fig. 1). The cause of the coloration is known to be due to impurities and / or imperfections:

- The color of natural BROWN diamonds is still under investigation, but this color might be due to the presence of extended defects, related to clusters of vacancies (or tiny "holes" inside the diamond structure! e.g. Fisher et al., 2009). These vacancy clusters might be formed during an event of plastic deformation: inside the Earth's mantle, the pressure conditions are extremely high, and stress can be applied to the minerals that are contained in the mantle. As underneath high pressure combined with high temperature, the minerals won't necessary break, but will be deformed. The deformation involves some re-arrangement of the atomic structure, creating "holes" or vacancies, which can migrate with time and temperature to find other vacancies inside the diamonds, forming the clusters. For the time being, this process of formation is still speculative.

- The YELLOW color of most yellow diamonds is due to nitrogen-related impurities for most (the N3 center, isolated nitrogen -type Ib-, e.g. Fritsch, 1998).

- The GREEN color is due to natural radiation (e.g. Fritsch, 1998), which happens by circulation of radioactive fluids.

- The BLUE color for most blue diamonds is related to the presence of boron (e.g. Fritsch, 1998; King et al., 1998, Gaillou et al., 2012), even in very small quantity (usually less than one boron atom per million of carbon atoms is enough to give rise to a blue color). Some scientific details are given below.

- The GREY to GRAYISH-BLUE to VIOLET colors typical of some diamonds from the deposit of Argyle, in Australia is most likely associated with the presence of hydrogen impurities (Fristch & Scarratt, 1992; Van Der Bogert et al., 2009; Goss et al., 2011).

- The "pure" ORANGE color (meaning, without any brown or yellow component) is highly rare, and the origin of the color is unknown.

- The exact origin of the PINK to RED colors is still a matter of speculation. We know that, as for brown diamonds, plastic deformation is involved. But the impurity and / or defect has not been identified yet. For more scientific details, see the paragraph below, or download the pdf of the article here.

I-1.THE NATURE OF THE PINK COLOR IN NATURAL DIAMONDS.

The origin of the pink color, which sometimes has a purple hue or a dark tone (sometimes described as “red”), is still not completely understood. Plastic deformation is known to play an important role in the development of pink lamellae or “graining” within colorless diamonds (Fig. 1). The color is the result of a broad absorption band centered at about 550-560 nm that absorbs most of the visible spectrum except for the red. Thus far, the cause of this absorption feature is unknown, and unfortunately, the center, or other defect that is responsible for the absorption does not seem to be active in any other spectroscopic mode.

In our study (Gaillou et al., 2010), we recognized that there are two distinct groups of type Ia (that is, containing nitrogen impurities in aggregate states) natural pink diamonds:

- group 1: Natural pink diamonds from Argyle in Australia and from Santa Elena in Venezuela. For these diamonds, the pink color is widespread, forming wavy bands inside a colorless diamond (see Fig. 2 & 3).

Fig. 2: A pink diamond from Argyle, Australia.

Fig. 3: Slice of pink diamond from Argyle, polished perpendicularly to the pink graining. Wavy bands of colorless/pink areas are visible.

- group 2: Natural pink diamonds from other localities (including: Canada, Russia, Siberia, South Africa and Tanzania). For these diamonds, the pink color is restricted to thin pink lamellae in a colorless diamond (see Fig. 3).

Fig. 4: Rough diamond from Brazil.

Fig. 5: Slice of pink diamond (group 2).

These 2 groups present spectroscopic features that are different (by Raman spectroscopy, cathodoluminescence, photoluminescence); they are extensively described in Gaillou et al. (2010). Examples of cathodoluminescence imagery are given in Fig. 6 & 7. In all cases though, all the defects involved nitrogen aggregates associated with vacancies (such as the new 405.5 nm center and the well known H3 center).

Fig. 6: Cathodoluminescence picture of a pink Argyle diamond (group 1). In blue: growth sectors (N3 centers), in green: H3 centers describing a "fish-scale" pattern.

Fig. 7: Cathodoluminescence image of a pink diamond (group 2). The pink lamellae emit a green CL (H3 centers + less intense 405.5 nm center), the colorless diamond emit a blue luminescence (from the "blue band", also called "band A").

For the second group of diamond, it was recently suggested (Mineeva et al., 2009) and then confirmed (Gaillou et al., 2010; Titkov et al., 2012) that plastic deformation and subsequent annealing is manifested by the presence of pairs of twin planes. No similar studies have been conducted on group 1 diamonds so far, so we can only speculate that similar processes happen for group 2 diamonds.

We therefore proposed that to accommodate deformation, mechanical twinning takes place, which also creates vacancies. With time and the high temperature existing in the Earth's mantle, the vacancies created at the twins can move to the next nitrogen aggregates (here, most likely A-aggregates) to form the new 405.5 nm center, the H3 center, and the center responsible for the pink color. 

To learn more about this, dowload the pdf of the article.

I-2. BORON CONTENT IN NATURAL BLUE DIAMONDS.

Fig. 8: A natural blue diamond.

Boron is known to be the coloring agent in blue diamonds (Fig. 8), as this element causes a strong absorption in the infrared, tailing off in the visible range. However, the concentration of boron is reported to be very low (less than 0.5 ppm) in natural diamonds, and therefore difficult to measure. That is probably why most of the works conducted on boron in diamonds have been done on synthetic, boron doped diamonds, which can contain boron up to about 1,000 ppm. An indirect way to measure boron is to use the intensity of some absorption lines in the infrared to calculate the boron concentration. But this method does not take into account the boron that might interact with other possible impurities (such as nitrogen or hydrogen) and that will be inactive in the infrared: only the so-called uncompensated boron is visible. Our work consists in comparing the different methods of measuring boron in natural blue diamonds, and to develop a new method of direct chemical analyses of the total boron content by Time-of-Flight SIMS (ToF-SIMS; Fig. 9). This method is nearly non-destructive, and we were able to conduct the analyses on extremely valuable samples, such as the HOPE, the BLUE HEART and the CULLINAN blue diamonds.

Fig. 9: ToF SIMS of the Smithsonian Institution, with which Boron measurements were conducted.

Uncompensated boron (as seen by Infrared Spectroscopy) + compensated boron (meaning, associated to other defects, such as nitrogen) = total boron (as seen by ToF SIMS).

Infrared spectroscopy measurements reveal uncompensated boron values as large as 1.72 ± 0.15 ppm, which is significantly higher than the previously reported maximum of 0.5 ppm. ToF-SIMS analyses gave spot total boron concentrations as high as 8.4 ± 1.1 ppm for the Hope diamond to less than 0.08 ppm in other blue diamonds. By comparison, a type Ia diamond did not show detectable boron. ToF-SIMS analyses revealed strong zoning of boron in some diamonds, which was confirmed by mapping the uncompensated boron using synchrotron infrared spectroscopy. This greater range of boron concentrations compared to previous studies might be explained by the larger number of natural diamonds analyzed here, 78, compared to <10 samples reported in the literature. The samples in this study are all gem-quality diamonds, including some Intense to Fancy-Deep blue diamonds; color intensity, however, only loosely correlates with the boron content. Boron is also likely responsible for the phosphorescence emissions of type IIb diamonds, in the red at 660 nm and in the blue-green at 500 nm (Fig. 10). Our results are consistent with previous work suggesting that the emissions are caused by donor-acceptor pair recombination processes involving boron and other defects. The exact nature of the phosphorescence processes is still not fully understood, but likely involves complex steps of charge carrier trapping and detrapping.

Fig. 10: Phosphorescence spectrum for a typical blue diamond: The emission is dominated by a short blue band at 500nm, with a less intense red 660 nm band. In the case of the Hope and Wittelsbach diamonds, the red band dominates.

I-3. DIAMONDS IN THE NATIONAL GEM COLLECTION.

The National Museum of Natural History gave me a unique opportunity during my postdoc position at the Smithsonian to look at incredible gems and minerals. Part of the work I have been conducted involves the characterization of some of the diamonds of the National Gem Collection, such as the Napoléon Diamond Necklace, or diamonds that were temporary on loan to the Museum, such as the Wittelsbach-Graff diamond.

 II- THE ORIGIN OF DIAMONDS

Under construction.

III- PUBLICATION LIST

III-1. PEER REVIEWED PUBLICATIONS

Gaillou E., Post J.E., Butler J.E. (2012)Boron in natural type IIb blue diamonds: chemical and spectroscopic measurements. American Mineralogist, Vol. 97, No 1, 1-18.

Gaillou E., Fritsch E., Massuyeau F. (2012) Luminescence of gem opals: a review of intrinsic and extrinsic emission. Australian Gemmologist, Vol. 24, No 8, pp. 200-201.

Rondeau B., Cenki-Tok B., Fritsch E., Mazzero F., Gauthier J.-P., Bodeur Y., Bekele E., Gaillou E., Ayalew D. (2011) Geochemical and petrological characterization of gem opals from Wegel Tena, Wollo, Ethiopia: opal formation in an oligocene soil. Geochemistry: Exploration, Environment, Analysis, In Press.

Walter M.J., Kohn S.C., Araujo D., Bulanova G.P., Smith C.B., Gaillou E., Wang J., Steele A., Shirey S.B. (2011)Deep mantle cycling of oceanic crust: evidence from diamonds and their mineral inclusions. Science, vol. 334, No 6052, pp. 54-57.

Gaillou E., Post J.E., Wang W., King J.M., Moses T.M., Butler J.E. (2010) More on the Wittelsbach-Graff and Hope diamonds. Gems & Gemology, vol. 46, No 3, pp. S1, S4.

Gaillou E., Post J.E., Bassim N., Fries M., Rose T., Stroud R., Butler J.E. (2010) Spectroscopic and microscopic characterization of color lamellae in natural pink diamonds. Diamond & Related Materials, vol. 19, pp. 1207-1220.

Gaillou E., Wang W, Post J.E., King J.M., Butler J.E., Collins A.T., Moses T.M. (2010)The Wittelsbach-Graff and Hope diamonds: not cut from the same rough. Gems & Gemology, vol. 46, No 2, pp 80-88.

Rondeau B., Fritsch E., Mazzero F., Gauthier J.-P., Cenki-Tok B., Bekele E., Gaillou E. (2010) Play-of-color opal from Wegel Tena, Wollo Province, Ethiopia. Gems & Gemology, vol. 46, No 2, pp 90-105.

Gaillou E., Fritsch E., Aguilar-Reyes B., Rondeau B., Barreau A., Ostroumov M. (2008) Common gem opal: An investigation of micro- to nano-structure. American Mineralogist, vol. 93, pp. 1865-1873.

Gaillou E., Fritsch E., Notari F. (2008) Photoinduced absorptions of the H1b and H1c centers in some natural treated diamonds. Diamond and Related Materials, vol. 17, pp. 2029-2036.

Gaillou E., Delaunay A., Rondeau B., Bouhnik-Le Coz M., Fritsch E., Cornen G., Monnier C. (2008) The geochemistry of opals as evidence of their origin. Ore and Geology Reviews, vol. 34, pp. 113-126.

Gaillou E., Post J.E. (2008) An examination of the Napoléon diamond necklace. Gems and Gemology, vol. 43, n° 4, pp. 352-357. http://lgdl.gia.edu/pdfs/gemsandgemology/articles/Wi07-G&G-article-on-napoleon-diamond-necklace.pdf

Karampelas S., Gaillou E., Fritsch E., Douman M. (2007) Color-zoned andradite-demantoid from Iran, with calcite inclusions. Gems and Gemology, vol. 43, n° 1, pp. 65-67 .

Fritsch E., Gaillou E., Rondeau B., Barreau A., Albertini D., Ostroumov M. (2006) The nanostructure of fire opal. Journal of Non Crystalline Solids, vol. 352, pp. 3957-3960.

Gaillou E., Delaunay A., Fritsch E., Bouhnik-le-Coz M. (2006) Geologic origin of opals deduced from geochemistry. Gems & Gemology, vol. 42, n°3, p. 107.

Gaillou E., Rondeau B., Fritsch E., Bouhnik-Le-Coz M., Cornen G., Ostroumov M. (2005) Toward a geochemistry of opals. Geochimica et Cosmochimica Acta, vol. 69, n° 10, p. A279.

Gaillou E., Mocquet B., Fritsch E. (2004) A new material from Madagascar: A mixture of cristobalite and opal. Gems & Gemology, vol. 40, n° 4, pp. 339-340.

Fritsch E., Gaillou E., Ostroumov M., Rondeau B., Devouard B., Barreau A. (2004) Relationship between nanostructure and optical absorption in fibrous pink opals from Mexico and Peru. European Journal of Mineralogy, vol. 16, pp. 743-752.

III-2. OTHER PUBLICATIONS

Gaillou E.,Devouard B., Vielzeuf D., Boivin P., Rochault J., Valley J., Harris C. (2010)Les saphirs du Mont Coupet, de Menet et du Sioulot : trois gisements du Massif Central à caractéristiques pétrogénétiques contrastées. Le Règne Minéral, vol. 93, pp. 28-36.

Gaillou E, Post J.E. (2008)Smithsonian collection provides treasure store of gemstones. InColor, Spring 2008, pp. 31-34.

Karampelas S., Gaillou E., Fritsch E., Douman M. (2007) Les grenats andradites-démantoïdes d’Iran : zonage de couleur et inclusions. Revue de gemmologie a.f.g., vol. 160, pp. 14-20.

Gaillou E. (2006) L’opale : un nanomatériau naturel. Mensuel de l’Université, n°11, section « Études » (online only at  http://www.lemensuel.net/L-opale-un-nanomateriau-naturel.html).

Gaillou E. (2006) Relations entre nanostructure, propriétés physiques et mode de formation des opales A et CT. Université de Nantes, France, PhD Thesis, 307pp.  http://www.gemnantes.fr/recherche/theses/files/gaillou.php

Gaillou E. (2005) Nouvelles absorptions photoinduites dans les diamants : H1b, H1c et système à 4850 cm^-1. Thesis of Gemological Diploma (diplôme d’Université de gemmologie), Université de Nantes, France, 50pp.           . http://www.gemnantes.fr/documents/pdf/DUGs/Gaillou_DUG.pdf

Gaillou E. (2005) Nouvelles absorptions photoinduites dans le diamant : H1b, H1c et système à 4850 cm^-1. Revue de gemmologie a.f.g., n° 155, p. 23.

Gaillou E. (2003) Étude minéralogique des saphirs du Sioulot, du Mont Coupet et de Menoyre ; détermination de leur origine géologique. Diplôme d’études approfondies, Université Blaise Pascal, France, 66pp. http://www.gemnantes.fr/documents/pdf/theses/DEA-Gaillou.pdf

III-3. CONFERENCES AND ABSTRACTS

Gaillou E., Shirey S.B.,  Bulanova G.P., Marks B., Smith C.B., Wang J., Kohn S.C., Walter M.J.. (2012) Sulfide inclusion re-os ages and carbon, nitrogen of diamonds from the Murowa kimberlites: implications for Zimbabwe craton evolution. 10^th International Kimberlite Conference Extended Abstract No. 10IKC-212.

Bulanova G.P., Marks A., Smith C.B., Kohn S.C., Walter M.J., Gaillou E., Shirey S.B., Trautman R., Griffin B.J. (2012) Diamonds from Sese and Murowa kimberlites (Zimbabwe) – evidence of extreme peridotitic lithosphere depletion and Ti-REE metasomatism.

Gaillou E., Post J.E., Rose T., Butler J.E. (2011)Cathodoluminescence applied to natural, plastically deformed diamonds: low temperature and high spatial resolution matter. Cathodoluminescence 2011, Microanalysis Topic Conference, October 25-25 2011, Gaithersburg, MD (lecture). Abstract published by Microscopy and Microanalysis.

Gaillou E., Post J.E., Butler J.E. (2011)On the peculiarities of Australian and Venezuelan pink diamonds: influence of the geologic settings. Goldschmidt Conference, Prague, Czech Republick, August 14^th-19^th 2011. Abstract in Mineralogical Magazine, 75, 3,p. 882 (lecture).

Gaillou E., Post J.E., Rost D., Butler J.E. (2011)Boron concentration in natural type IIb blue diamond. Diamond Conference, Warwick, UK, July 4^th-7^th 2011. Extended abstract in book of abstract, not published: The 62^nd Diamond Conference, Warwick 2011, pp O23.1-O23.3 (lecture).

Gaillou E., Post J.E., Steele A., Butler J.E. (2011) On the peculiarities of Australian and Venezuelan pink diamonds: influence of the geologic settings? Diamond Conference, Warwick, UK, July 4^th-7^th 2011. Extended abstract in book of abstract, not published: The 62^nd Diamond Conference, Warwick 2011, pp O18.1-O18.3 (lecture).

Rondeau B., Fritsch E., Gauthier J.-P., Mazzero F., Bodeur Y., Cenki-Tok B., Gaillou E., Bekele E. (2010)Sur les conditions de genèse des opales du Wollo (Ethiopie). 23ème Réunion des Sciences de la Terre (RST 2010), Bordeaux, France, October 25^th-29^th 2010. Session 4-1: Gemology (lecture).

Devouard B., Paquette J.-L., Ricci J., Médard E., Boivin  P., Gaillou E., Vielzeuf D., Rochault J. (2010) Saphirs et zircons gemmes d’Auvergne (Massif Central français) : occurrences, pétrogenèse, et géochronologie. 23ème Réunion des Sciences de la Terre (RST 2010), Bordeaux, France, October 25^th-29^th 2010. Session 4-1: Gemology (lecture).

Gaillou E., Rost D., Post J.E., Butler J.E. (2010)Quantifying Boron in Natural Type IIb Blue Diamonds. Goldschmidt Conference, Tennessee, Knoxville, June 13^th-18^th 2010. Abstract in Geochimica et Cosmochimica Acta, 74, 12, p. A313 (lecture).

Fritsch E., Gaillou E., Massuyeau F. & Rondeau B. (2010) Luminescence of Opals: A Witness to their Geochemistry. Goldschmidt Conference, Tennessee, Knoxville, June 13^th-18^th Juin 2010. Abstract in Geochimica et Cosmochimica Acta, 74, 12, p. A307 (lecture).

Fritsch E., Gaillou E., Massuyeau F. (2009) Luminescence of opals: a review of intrinsic and extrinsic emission. International Gemmological Conference, Arusha, Tanzanie. Abstract in Proceedings book. pp 17-18. 10-14 October (lecture).

Gaillou E., Post J.E., Bassim N., Rose T., Fries M., Stroud R., Butler J.E. (2009) Nature of the pink graining in natural diamonds. Diamond Conference, Warwick, UK, July 7^th-10^th 2009. Extended abstract in book of abstract, not published: The 60^th Diamond Conference, Warwick 2009, pp P34.1-P34.3 (poster).

Post J.E., Gaillou E., Eaton-Magana S., Butler J.E. (2009)Smithsonian Diamonds: Science and Lore. Diamond Conference, Warwick, UK, July 7^th-10^th 2009. Extended abstract in book of abstract, not published: The 60^th Diamond Conference, Warwick 2009, pp PI1.1-I1.2 (lecture).

Gaillou E., Post J. E., Vicenzi E.  P., Rose T., Bassim N., Stroud R. M., Butler J. E. (2008)Optical characterization of natural pink diamonds: a study of the type Ia non-Argyle pinks. Diamond Conference, Oxford, UK, 7-9^th July 2008 (lecture #28). Extended abstract in book of abstract, not published: The 59^th Diamond Conference, Oxford 2008, pp 28.1-28.3 (lecture).

Gaillou E. (2008) Color in gem opals. Conference at the Mineralogical Society of Washington DC, April 2^nd. Invited speaker. Abstract in: Mineral Minutes (Mineralogical Society of the District of Columbia), vol. 67, No 5, pp.4-5.

Gaillou E. (2008) Color in gem opals. 1417^th Meeting of the Geological Society of Washington, January 23^rd, Washington, DC, USA. Invited speaker.

Gaillou E. (2008) An examination of the Napoléon necklace. Mineral Sciences lecture, Smithsonian Institution, June 6^th, 2008.

Gaillou E., Fritsch E., Notari F. (2007)Photoinduced absorptions of the H1b and H1c centers in some natural treated diamonds. Diamond Conference, Warwick, UK, July 11^th-13^th 2007 (poster P10). Extended abstract in book of abstract, not published: The 58^th Diamond Conference, Warwick 2007, pp. P10.1-P10.2 (poster).

Fritsch E., Gaillou E., Rondeau B., Ostroumov M., Aguilar-Reyes B., Barreau A., Albertini D. (2007) Shining new lights on opals. Annual Conference of the Scottish Branch of Gemmological Association, May 4^th-7^th 2007 (lecture).

Fritsch E., Rondeau B., Gaillou E., Gauthier J.-P., Massi L. (2007)Questions actuelles sur l’apparence colorée des matériaux gemmes. GDR Couleur, March 14^th, CNRS, Paris, France (lecture).

Gaillou E. (2006) Inclusions minérales dans les saphirs : aide à la détermination de l’origine géologique et géographique. Scientific days on vitreous inclusions, Nancy, France, Novembre 30^th and Decembre 1^st 2006 (lecture). Invited speaker.

Gaillou E., Delaunay A. Fritsch E., Bounik-Le Coz M. (2006) Geologic origin of opals deduced from geochemistry. Gemological Research Conference (GRC), August 26^th-27^th, San Diego, California, U.S.A (lecture).

Gaillou E., Fritsch E., Notari F. (2005) New photoinduced absorptions in diamonds: H1b, H1c and 4850 cm^-1 system. Diamond 2005, 16th European Conference on Diamond, Diamond-like Materials, Carbon Nanotubes and Nitrides, Toulouse, France, Septembre 11^th-16^th 2005. Abstract in the book of abstracts, unpublished, ref [15.4.10] (poster), p. 15.4.10.

Gaillou E., Rondeau B., Fritsch E., Bouhnik-Le-Coz M., Cornen G., Ostroumov M. (2005) Toward a geochemistry of opals. Goldschmidt Conference 2005, 20-25 May, Moscow, Idaho, USA (lecture).

Gaillou E., Fritsch E., Rondeau B., Aguilar B.O., Faulques E., Ostroumov M. (2005) L’opale, un nanomatériau naturel. Colloque Matériaux Pays de la Loire. La Chapelle/Erdre, Juillet 8^th-9^th (poster).

Gaillou E. (2005) Les saphirs magmatiques du Massif Central. VI^es Rendez-Vous Gemmologiques de Paris, March 5^th, Paris, France (lecture). Invited speaker.

Fritsch E., Ostroumov M., Rondeau B., Aguilar-Reyes B.O., Barreau A., Gaillou E., Albertini D., Wery J. (2003) Nano- to micro-structure of natural gem opals: relation to deposition and growth conditions. Materials Research Society Fall 2003. Boston, MA, USA (lecture).