Evan M. Smith

• PhD, MEng, BEng
• Senior Research Scientist at Gemological Institute of America

Recently published experimental data suggest that the Earth’s mantle below ∼250 km is saturated in metallic Fe, reaching a concentration of ∼1 wt.% Fe0 throughout the lower mantle and buffering oxygen fugacity by Fe0↔Fe2+ reactions. Metallic Fe in the mantle bears important implications for N, which behaves as a moderately siderophile element. Here...

We analyzed the first samples of Neoarchean mantle fluid captured as inclusions in fibrous diamonds from the 2.701–2.697 Ga Wawa metaconglomerate (Canada). The K-, Na-, and Cl-rich carbonate-bearing saline fluid inclusions bear a strong resemblance to those of Phanerozoic fibrous diamonds. This similarity in major and trace elements, volatile com...

Diamonds rock their metal roots Massive diamonds are rare, expensive, and captivating. These diamonds now appear to be distinctive not only in their size but also in their origin. Smith et al. probed mineral inclusions from these very large diamonds and found abundant slivers of iron metal surrounded by reducing gases. This suggests that the large...

Geological pathways for the recycling of Earth’s surface materials into the mantle are both driven and obscured by plate tectonics1–3. Gauging the extent of this recycling is difficult because subducted crustal components are often released at relatively shallow depths, below arc volcanoes4–7. The conspicuous existence of blue boron-bearing diamond...

Subducting tectonic plates carry water and other surficial components into Earth’s interior. Previous studies suggest that serpentinized peridotite is a key part of deep recycling, but this geochemical pathway has not been directly traced. Here, we report Fe-Ni–rich metallic inclusions in sublithospheric diamonds from a depth of 360 to 750 km with...

Two diamond varieties are described in this review paper whose geological origin has only recently been illuminated. The first is large irregular Type IIa (nitrogen-poor) diamonds, which includes many famous, high-quality gems such as the Cullinan and the Koh-i-Noor. This variety has been named CLIPPIR (Cullinan-like, large, inclusion poor, pure, i...

RamanCrystalHunter (RCH) is a new software program designed to pre-process, analyze, and identify Raman spectra by comparison with spectra in the RamanCrystalHunter Database (RCHDB). The software is free and can be downloaded from the website https://www.fabrizionestola.com/rch. RCH is characterized by a simple graphical user interface, making it s...

Boron is a quintessential crustal element but its conspicuous presence in diamond-a mantle mineral-raises questions about potential subduction pathways for boron and other volatiles. It has been a long-standing goal to characterize the isotopic composition of boron in blue, boron-bearing (Type IIb) diamonds to reveal its origin. Mineral inclusions...

Some rare diamonds originate below the lithosphere, from depths of 300-800 km and perhaps deeper. Ongoing sublithospheric or super-deep diamond research is providing new insight into the mantle and the hidden consequences of plate tectonics. Here we highlight several advances in the past decade, stemming from the discovery of inclusions from oceani...

Some rare diamonds originate below the lithosphere, from depths of 300–800 km and perhaps deeper. Ongoing sublithospheric or super‐deep diamond research is providing new insight into the mantle and the hidden consequences of plate tectonics. Here we highlight several advances in the past decade, stemming from the discovery of inclusions from oceani...

Crowningshieldite is the natural analog of the synthetic compound α-NiS. It has a NiAs-type structure and is the high-temperature polymorph relative to millerite (β-NiS), with an inversion temperature of 379 °C. Crowningshieldite is hexagonal, space group P63/mmc, with a = 3.44(1) Å, c = 5.36(1) Å, V = 55.0(2) Å3, and Z = 2. It has an empirical for...

Pre-print available for download. For published copy, see the Mineralogical Association of Canada: https://www.mineralogicalassociation.ca/publications/topics-in-mineral-sciences/tms49/

The science of studying diamond inclusions for understanding Earth history has developed significantly over the past decades, with new instrumentation and techniques applied to diamond sample archives revealing the stories contained within diamond inclusions. This chapter reviews what diamonds can tell us about the deep carbon cycle over the course...

“Super-deep” diamonds are thought to have a sub-lithospheric origin (i.e. below ~300 km depth) because some of the mineral phases entrapped within them as inclusions are considered to be the products of retrograde transformation from lower-mantle or transition-zone precursors. CaSiO3-walstromite, the most abundant Ca-bearing mineral inclusion found...

SEM and EPMA Analyses of Metallic Inclusions in Diamonds - Probing the Earth’s Deep Mantle - Volume 23 Issue S1 - Emma S. Bullock, Evan M. Smith, Steven B Shirey

Full text available: https://www.gia.edu/gems-gemology/summer-2017-labnotes-diamond-concentric-inclusions

Large and relatively pure diamonds like the historic 3,106 ct Cullinan, found in South Africa in 1905, have long been regarded as unusual based on their physical characteristics. For example, they often exhibit exceptional color and clarity, while routinely qualifying as type IIa, a rare designation of chemical purity. A new research discovery abou...

Full text available: https://www.gia.edu/gems-gemology/winter-2017-labnotes-lizard-skin-deformed-diamond

Full text available: https://www.gia.edu/gems-gemology/winter-2016-microworld-ferropericlase-inclusion-diamond

Full text available: https://www.gia.edu/gems-gemology/spring-2016-labnotes-diamond-inclusion-radiation-halo

Full text available: https://www.gia.edu/gems-gemology/winter-2016-labnotes-coesite-inclusions-filaments-diamond

Fluid inclusions were studied in six octahedrally-grown, eclogitic diamonds from the Ebelyakh River mine, northern Russia, using microthermometry and Raman spectroscopy. The fluids are CO2–N2 mixtures with 40 ± 4 mol% N2, which are trapped along fractures that healed in the diamond stability field. The CO2-rich composition of the fluids provides th...

We analyzed mineral microinclusions in fibrous diamonds from the Wawa metaconglomerate (Superior craton) and Diavik kimberlites (Slave craton) and compared them with published compositions of large mineral inclusions in non-fibrous diamonds from these localities. The comparison, together with similar datasets available for Ekati and Koffiefontein k...

Transmission X-ray diffraction is demonstrated as a new tool for examining daughter minerals within sub-micrometre-size fluid inclusions in fibrous diamond. In transmission geometry, the X-ray beam passes through the sample, interacting with a volume of material. Fibrous diamonds from Mbuji-Mayi, Democratic Republic of Congo; the Wawa area, Ontario...

The common brown color in natural diamond is likely caused by vacancy clusters, produced by plastic deformation of the crystal structure. A brief treatment in a high-pressure - high-temperature (HPHT) vessel at 180O-2700°C can remove this color. As there has been speculation that a similar removal of color should occur continuously at depth in the...

Fibrous diamond, occurring both as cuboids and as coatings over non-fibrous diamond nuclei, is translucent due to the presence of millions of sub-micron-sized mineral and fluid inclusions. Diamond is strong and relatively inert, making it an excellent vessel to preserve trapped materials. These microinclusions represent direct samples of natural di...

Brown colour in natural diamonds is produced by plastic deformation during residence in the mantle. Dislocation movement generates vacancies, which aggregate into clusters of about 30-60 vacancies. The resulting electronic configuration at each cluster leads to the broad, featureless absorption pattern associated with common brown colour. Less comm...