Classification of brown diamonds and their color origin - GemNantes

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4) Chalky blue luminescence (4 stones) 5) Reddish orange emission (3 stones) 6) Orangy yellow emission (1 stone) 7) Strong yellowish green fluorescence (1) The strength of the luminescent glow was generally faint to weak, except for the group exhibiting the yellow fluorescence with phosphorescence- these diamonds exhibited a medium to medium strong emission, which was irregularly distributed. Also, near-pure IaB diamonds showed a medium-strong (blue) glow and the H3 center in diamond #11 causes a strong yellowish green fluorescence. The strength of the blue fluorescence in some of the analyzed brown diamonds followed the grain bands. 3.4. Observations with magnification 3.4.1. Inclusions The observation of the internal features present in the diamonds revealed, that there are basically three types of characteristic inclusion-scenarios present: 1) Fractures (“feathers”) and relatively “large” crystals (Fig.10) Figure 10. Crystals in a type Ia diamond 2) Large amounts of tiny reflective flakes (some with hexagonal outline) often associated with very fine needle-like inclusions (Fig. 11) Figure 11. Reflecting particles, one with a clearly hexagonal shape 9
3) Tiny particles forming a phantom (Fig. 12) Figure 12. A cuboid phantom formed by tiny particles The first type was observed in all of the 20 “typical” brown diamonds and some of the “specials”; by far most of these stones only contained feathers and crystals were rather rare. The second type was only seen in the “special” diamonds-it was limited to the diamonds with yellow fluorescence and lasting phosphorescence. The third type is very rare and has only been seen in some type Ib brown diamonds. 3.4.2. Pattern observed under crossed polarizing filters Although diamonds are isotropic, they frequently exhibit anomalous double refraction (ADR), when observed under crossed polarizing filters. It has been reported, that especially brown diamonds are always highly strained (Shigley and Fritsch, 1993). Such strain will manifests itself as interference colors when a stone is viewed under crossed polarizing filters (Fig. 13). ADR can be seen as tatami and banded extinction patterns with usually the above mentioned interference colors (Smith et al, 2000). This indicates that these diamonds are not perfectly isotropic. Figure 13. Strain clearly distributed along olive-brown graining (left, 30x, crossed polarizers, right, 30x, immersion) Strain of various degrees has been observed in all 63 brown diamonds except the stones with the yellow fluorescence/lasting phosphorescence. The strain pattern was generally clearly distributed along the brown graining (e.g. sample 12, Fig. 13). In some cases, the strain was quite random though and appeared as a mottled, curved and twisting pattern (Fig. 14) without an apparent orientation. 10
Page 1 and 2: 2003 DIPLÔME D’UNIVERSITÉ DE GE
Page 3 and 4: 5. Suggested classification of brow
Page 5 and 6: 1. Introduction Brown diamonds are
Page 7 and 8: extremely difficult to observe and
Page 9: 7) Color partly patchy or homogeneo
Page 13 and 14: sometimes absorptions due to positi
Page 15 and 16: Figure 17. The distinct amber cente
Page 17 and 18: Figure 20. The IR spectrum of a “
Page 19 and 20: More diamonds of a brown coloration
Page 21 and 22: Figure 26. This “Pseudo-CO2” di
Page 24 and 25: 3.5.4. Peak Table: FTIR spectra Sam
Page 26 and 27: 3.6. VIS/NIR Spectroscopy The spect
Page 28 and 29: produced at temperatures ~ 2100°C.
Page 30 and 31: Figure 33. The spectrum of the smal
Page 32 and 33: Figure 37. The spectrum of a type I
Page 34 and 35: Figure 39. The low temperature PL s
Page 36 and 37: Figure 43. A typical PL spectrum fo
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Page 40 and 41: 3.9. Cathodoluminescence The cathod
Page 42 and 43: 4.1. Table of Properties sample # w
Page 44 and 45: sample # weight ct type (FTIR), IR
Page 46 and 47: Another very apparent correlation w
Page 48 and 49: Figure 53. The IR spectra of diamon
Page 50 and 51: 4.6. IR type VS. inclusions There w
Page 52 and 53: # FTIR Color appearance Pattern bet
Page 54 and 55: # FTIR Color description Color appe
Page 56 and 57: # FTIR Color description Color appe
Page 58 and 59: # FTIR Color appearance Pattern bet
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# FTIR Color description Color appe
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# FTIR Color appearance Color descr
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4.10. Picture Table: Color distribu
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# FTIR Picture of color distributio
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5. Suggested classification of brow
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pattern following the phantom. The
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Regular type Ib (“culet” prepar
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“Pseudo-CO 2 ” (type Ia) (“cu
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7. HPHT annealing of brown diamonds
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absorption was reduced. The type Ia
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Type Ia, type Ib/aA • only brown
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Koivula, J.I. (2000) The Micro Worl
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Classification of brown diamonds and their color origin - GemNantes

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