An update of Algerian’s seismic catalog from historical seismicity, archeoseismological, and paleoseismological studies

For any seismic hazard study, a reliable, homogenized, and complete seismic catalog is required. The Algerian seismicity catalog has been recently updated by retrieving and reappraising many historical events. The Algerian seismic network has also been densified up to about 80 seismic stations covering the Tell Atlas which is the most active area of northern Algeria for monitoring of the seismic activity reducing the magnitude threshold. Recently, we have launched archeoseismological studies to retrieve past strong earthquakes that have affected Roman sites located along the Tell Atlas. Here, we proceed with tectonic investigations around selected sites where significant observed damage were identified. On the other hand, paleoseismological investigations were conducted along the El Asnam fault (now Chlef) following the large Ms 7.3 earthquake of 1980. Paleoseismic studies combined with archeoseismological results provide the dating of past earthquakes and contribute to the completeness of the seismicity catalog.This work was prepared with the support of UNESCO-IGCP-659 Project “Seismic Hazard and Risk in Africa”

An Historical Alexandrite from the Mineralogy Museum of Paris School of Mines

International audienceA spectacular 42.54 ct faceted alexandrite belonging to the collection of the Mineralogy Museum of Paris School of Mines was non-destructively characterised for this report. This historical gem was exhibited in at least one exposition in Paris during the late 1870s and/or in 1880 before it was donated to the museum by lapidary Henri Garreaud in 1882. However, its geographic origin was not stated, and its gemmological properties have not been examined until now. Our study reveals that the gem's microscopic, chemical and spectroscopic characteristics are similar to those of alexandrite from Sri Lanka

A historical alexandrite at Paris School of Mines

International audienceKept in the vault since its donation to the museum in 1882, a 42.54 ct alexandrite (Fig. 1) will finally be revealed in 2023 during a temporary exhibition at the Mineralogy Museum of Mines Paris - PSL (Paris School of Mines), France. The reasons why this exceptional stone was never exhibited are not well constrained, but we can hypothesize that 1- the value of the gem was too high and as a safety precaution it was kept in the vault, 2- it was too difficult to properly exhibit the stone to show its change-of-color, 3- at the time of its arrival, gems were not of interest to the curatorial staff (M. Ernest Mallard).The opportunity to show off this rare collector’s stone is eventually found: a temporary exhibit is under development and will highlight important historical stones, including this hidden treasure. The exhibit untitled “Minerals - Objects of Collection”, meant to open mid-2023, will display the different ways through which the museum’s collection grew: donations, purchases, exchanges, custodies, confiscations and field trips. The alexandrite will be presented in its own showcase as a “secret revealed” from the collection, in the donations theme.Before being exhibited, the alexandrite is undergoing a research project: its history is being investigated and its gemological properties characterized. This investigation is part of an ongoing project on the study of historic gems of the Mineralogy Museum of Mines Paris - PSL, in partnership with the French Gemological Laboratory (LFG). The classical gem characterization was conducted at the museum while the microscopic, chemical and spectroscopic analyses at the LFG in Paris, respecting time constraint due to security reasons. In this lecture, we will present its journey before arriving at the museum, from the gem cutter that faceted it, exhibited it at the World Fair in Paris in 1878, and eventually donated it to the museum fou

The Beni Haoua, Algeria, Mw 4.9 earthquake: source parameters, engineering, and seismotectonic implications

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GEMMOLOGICAL AND SPECTROSCOPIC STUDY WITH MOBILE INSTRUMENTS OF THE “EMERALDS” FROM THE FRENCH CROWN JEWELS

International audienceRare are the scientific studies on gemstones from the French Crown Jewels, for the good reason that most of them were sold away by the French Third Republic in 1887, to get rid of this symbol of Royalty and Empire. Some unset stones were however put aside from the big sell, and given to some French museums, including the French Natural History Museum, the Louvre, and the Paris School of Mines. Some jewels have been bought back since the late 20 th by the Louvre, but mostly, the Crown Jewels are still spread out around the world. This paper is part of an ongoing project on the study of the French Crown Jewels owned the Paris School of Mines since 1887, in collaboration with the French Gemmological Laboratory (LFG). As this National Treasure is security sensitive, the project had to be conducted on site at the MINES Paristech Mineralogy Museum, using portable analytical instruments. In this first study, we are presenting the results acquired on some green coloured gems that used to be part of the coronation Crown of Napoleon III

Gemological study of emeralds from the Crown of Napoleon III at Paris School of Mines

International audienceAs most of the French Crown Jewels, the Coronation Crown of Napoleon III was dismantled in 1887 prior to the large auction intended to get rid of the foremost symbol of Royalty and Empire. The crown was created by the Emperor's jeweler, Alexandre Gabriel Lemonnier in 1855, depicting 8 golden eagles and palm leafs, adorned with diamonds and emeralds. The large 8 emeralds were given back to the Empress Eugenie, while the large 8 diamonds and other smaller diamonds were sold in 1887. The smaller 50 emeralds were put aside and donated to the Ecole Nationale Supérieure des Mines de Paris-Paris School of Minesbefore the auction (Morel, 1988). Lemonnier also created a similar but smaller crown for Empress Eugenie, which was kept in her family and eventually donated to the Louvre museum in 1988. In this study, we are reporting for the first time a gemological study of the remaining 45 emeralds in the collection of Paris School of Mines (Figure 1: 8 main emeralds, ENSMP69866). Our examination revealed that 41 out of 45 gems were indeed natural emeralds, presenting no evidence of clarity enhancement. Because of their gemological characteristics, we could established their provenance to most likely be Colombia, especially that they were mounted in 1855. Four samples however found to be artificial glass, possibly set on the crown since the beginning. This study is part of a worldwide intention of studying gemstones of historical meaning and significance

Spectroscopic Study of Egyptian Emeralds

International audienceEmeralds have been known since ancient times (dated 2000 BCE) and they appear commonly in jewelry [1]. The most important and historic occurrences of emeralds in Egypt are in the Wadi Nugrus and Zabara areas [2]. The deposit of emeralds can be found in quartz or pegmatite veins which come from partial melting of metasedimentary rocks. These veins are in contact with biotite schists. The later tectonic and metasomatic events led to deformational effects and the albitization of the host rock [3]. This later metamorphic episode transformed the pre-existing Type IA (from Mafic-Ultramafic rocks) emerald deposits into Type IID (Metamorphosed type I deposits with hidden-granitic intrusion) [4]. Spectroscopic data on emeralds from Egypt are scarce. In the present study various non-destructive spectroscopic methods, such as Raman, FTIR, UV-Vis-NIR, and EDXRF along with classic gemmological means, were applied on 8 samples from the Ecole des Mines (Mines Paris - PSL). All analytical methods were implemented at the LFG. Raman and FTIR methods revealed that Type II water in Egyptian emeralds is more intense than Type I water (Fig. 1). This result indicates that the water molecules (H2O) in the channels of the beryls’ structure are accompanied with the presence of alkali ions. Using EDXRF, low levels of Cs and Rb were detected. The UV-Vis-NIR analysis showed that the chromophore ions in Egyptian emeralds are mainly Cr+3and Fe+2. Under optical microscope and with Raman spectroscopy, quartz, calcite, feldspar, and mica were identified as associated minerals. Further research is currently ongoing, which will hopefully help to better understand the genesis of these emeralds

Non-Destructive Study of Egyptian Emeralds Preserved in the Collection of the Museum of the Ecole des Mines

In the present study, rough emerald single crystals and rough emeralds in the host rock from the ruins of Alexandria and from the Mount Zabargad in Egypt, preserved in the collection of the museum of the Ecole des Mines (Mines Paris—PSL) since the late 19th or early 20th century, are investigated. All samples were characterized by non-destructive spectroscopic and chemical methods during a week-long loan to the LFG. Raman, FTIR and UV-Vis-NIR spectroscopy revealed that Egyptian emeralds contain H2O molecules accompanied by relatively high concentrations of alkali ions and are colored by chromium and iron. Additionally, EDXRF showed that the emeralds from Egypt contain up to 84 ppm Rb and low amounts (below 200 ppm) of Cs. Inclusions and parts of the host rock were also observed under optical microscope and analyzed with Raman spectroscopy. Tube-like structures, quartz, calcite, dolomite, albite and phlogopite are associated minerals, and inclusions are identified in these historic emeralds from Egypt. This work will hopefully further contribute to the characterization of emeralds of archaeological significance

Non-Destructive Study of Egyptian Emeralds Preserved in the Collection of the Museum of the Ecole des Mines

In the present study, rough emerald single crystals and rough emeralds in the host rock from the ruins of Alexandria and from the Mount Zabargad in Egypt, preserved in the collection of the museum of the Ecole des Mines (Mines Paris—PSL) since the late 19th or early 20th century, are investigated. All samples were characterized by non-destructive spectroscopic and chemical methods during a week-long loan to the LFG. Raman, FTIR and UV-Vis-NIR spectroscopy revealed that Egyptian emeralds contain H2O molecules accompanied by relatively high concentrations of alkali ions and are colored by chromium and iron. Additionally, EDXRF showed that the emeralds from Egypt contain up to 84 ppm Rb and low amounts (below 200 ppm) of Cs. Inclusions and parts of the host rock were also observed under optical microscope and analyzed with Raman spectroscopy. Tube-like structures, quartz, calcite, dolomite, albite and phlogopite are associated minerals, and inclusions are identified in these historic emeralds from Egypt. This work will hopefully further contribute to the characterization of emeralds of archaeological significance

A Gemological and Spectroscopic Study with Mobile Instruments of “Emeralds” from the Coronation Crown of Napoleon III

International audienceForty-five “emeralds,” formerly set in the coronation crown of Napoleon III, were studied using nondestructive mobile spectroscopic and gemological means. Adorned with emeralds, diamonds, and gold, the crown was created in 1855 by royal jeweler Alexandre Gabriel Lemonnier but dismantled in 1887 for the auctioning of the French crown jewels. Some of the emeralds were donated to the École des Mines (Paris School of Mines, now known as Mines Paris - PSL) in 1887, prior to the auction. Our examination revealed that 41 out of 45 gems were indeed natural emeralds, presenting no evidence of clarity enhancement. Their gemological characteristics and age suggest a Colombian provenance. The other four samples were determined to be artificial glass containing iron and/or copper and possibly other chromophores. These glass imitations could have been set when the crown was created or shortly thereafter. This study is part of an effort to examine gemstones of historical meaning and significance worldwide