The Profile of Trace Elements, Including the Ree, in Gem-Quality Green Andradite From Classic Localities

Bocchio, Rosangela; Adamo, Ilaria; Diella, Valeria

doi:10.3749/canmin.48.5.1205

Cited by 17 publications

(26 citation statements)

References 25 publications

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“…In some crystals of andradite, the determined value exceeded 6 wt % Cr 2 O 3 [67], but the studied crystals only contain up to 2.3 wt % Cr 2 O 3 . However, this content is still significantly higher than in other demantoid occurrences around the world [21,30,47]. Moreover, demantoid from Dobšiná is enriched in V (up to 0.09 wt % V 2 O 3 from EMPA, 305-572 ppm from LA-ICP-MS) compared to other localities with V usually below the detection limit of EMPA and below 270 ppm determined by LA-ICP-MS [21,30,47].…”

Section: Discussionmentioning

confidence: 78%

“…Moreover, demantoid from Dobšiná is enriched in V (up to 0.09 wt % V 2 O 3 from EMPA, 305-572 ppm from LA-ICP-MS) compared to other localities with V usually below the detection limit of EMPA and below 270 ppm determined by LA-ICP-MS [21,30,47]. The As content between 10-22 ppm (although very close to the detection limit, were below detection limit on other localities [21]) and absence of REE (except very low Y), which are usually between 1-90 ppm [21] could also be a fingerprint feature for Dobšiná demantoid.…”

Section: Discussionmentioning

confidence: 90%

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Gem-Quality Green Cr-Bearing Andradite (var. Demantoid) from Dobšiná, Slovakia

et al. 2019

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Andradite, variety demantoid, is a rare gem mineral. We describe gem-quality garnet crystals from serpentinized harzburgites from Dobšiná, Slovakia which were faceted. Both the andradite samples were transparent, with a vitreous luster and a vivid green color. They were isotropic with refractive indices >1.81. The measured density ranged from 3.82 to 3.84 g·cm−3. Andradite var. demantoid appeared red under Chelsea filter observation. Both samples contained fibrous crystalline inclusions with the typical “horsetail” arrangement. The studied garnet had a strong Fe3+ dominant andradite composition with 1.72–1.85 apfu Fe3+, Cr3+ up to 0.15 apfu, Al3+ 0.03 to 0.04 apfu, V3+ up to 0.006 apfu substituted for Fe3+, Mn2+ up to 0.002 apfu, and Mg up to 0.04 apfu substituted for Ca. Raman spectrum of garnet showed three spectral regions containing relatively strong bands: I—352–371 cm−1, II—816–874 cm−1, and III—493–516 cm−1. The optical absorption spectrum as characterized by an intense band at 438 nm and two broad bands at 587 and 623 nm and last one at 861 nm, which were assigned to Fe3+ and Cr3+. Transmission was observed in the ultraviolet spectral region (<390 nm), near the infrared region (700–800 nm), and around 530 nm in the green region of visible light, resulting in the garnet’s green color.

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Section: Discussionmentioning

confidence: 78%

Section: Discussionmentioning

confidence: 90%

Gem-Quality Green Cr-Bearing Andradite (var. Demantoid) from Dobšiná, Slovakia

et al. 2019

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“…In contrast, andradite samples (2,7) show the enrichment in LREE with respect to HREE. As already discussed by [29] this behavior is controlled by crystal chemistry and indicate that in a calcic garnet the substitution of Fe 3+ for Al at the [Y] site enlarges the eightfold [X] site and favors the incorporation of LREE. Moreover, the positive Eu anomaly, more evident in sample 7 and in the andradite-rich areas of sample 3, implies the presence of Eu in the reduced form (Eu 2+ ) according with the reaction Fe 2+ + Eu 3+  Fe 3+ + Eu 2+ [30] and its fractionation from the HREE.…”

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confidence: 66%

“…The instrument consisted of a 193 nm Excimer laser (Geolas) coupled to an Agilent 8900 triple quadrupole ICPMS. The spot size was 55 µm, using NIST SRM 610 glass as an external standard and 29 Si as an internal standard, as analyzed by microprobe. Precision and accuracy estimated on the USGS basaltic glass standard BCR2 and NIST612 were better than 10%.…”

Section: Sample D 1 (Mm)mentioning

confidence: 99%

Garnets from Val d’Ala Rodingites, Piedmont, Italy: An Investigation of Their Gemological, Spectroscopic and Crystal Chemical Properties

et al. 2019

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In Val d’Ala (Piedmont, Western Alps, Italy), the more interesting rocks for the mineralogical research are represented by rodingites (rich in mineralized veins and fractures) associated with serpentinites in the eclogitized oceanic crust of Piemonte Zone, south of Gran Paradiso Massif. Among the vein-filling minerals, garnets are the most appreciated as mineral specimens and, in less degree despite their vivid and rich colors, for their potential as gem-quality materials. This study provides a complete gemological characterization of five faceted samples and offers new information by means of Synchrotron X-ray computed micro-tomography imaging gem features. Electron-probe microanalysis (EMPA) and laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) established that the chemical composition of garnets from different localities, resulted both close to pure andradite, enriched in light rare earth elements (LREE) with a positive Eu anomaly, and grossular-andradite solid solution (grandite), enriched in heavy rare earth elements (HREE). X-ray powder diffraction analyses indicate the possible coexistence of almost pure grossular and andradite. A spectroscopic approach, commonly used with gem-like material, by Raman and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, completes the characterization of the samples. The new data on the textural and geochemical features of the grandite and andradite garnets suggest local growth processes under various chemical and oxidation conditions of metasomatic and metamorphic fluids interacting with the host-rocks. Garnets represent long-lasting mineral records of the complex geological history of the Val d’Ala rodingitic dikes during their oceanic- and subduction-related metamorphic evolution.

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“…There, it is yellowgreen to green in color and the gem variety name for such crystals is known as demantoid. Other andradite occurrences are known and the crystals can deviate to various degrees from strict end-member andradite composition (e.g., Bocchio et al, 2010). Andradite-rich garnet, commonly in solid solution with grossular, can be found in nature.…”

Section: Introductionmentioning

confidence: 99%

Heat capacity and entropy behavior of andradite: a multi-sample and −methodological investigation

Geiger¹,

Dachs²,

Vielreicher³

et al. 2018

ejm

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Andradite, ideal end-member formula Ca 3 Fe 3þ 2 Si 3 O 12 , is one of the common rock-forming garnets found in the Earth's crust. There are several outstanding questions regarding andradite's thermodynamic and physical property behavior. Three issues are: i) Could there be differences in the thermodynamic properties, namely heat capacity, C p , between synthetic and natural andradite crystals, as observed in the Ca-garnet grossular, Ca 3 Al 2 Si 3 O 12 ? ii) What is the thermal nature of the low-temperature magnetic-phasetransition behavior of andradite? and iii) How quantitative are older published calorimetric (i.e., adiabatic and DSC) heat-capacity results? In this work, four natural nearly end-member single crystals and two synthetic polycrystalline andradite samples were carefully characterized by optical microscope examination, X-ray powder diffraction, microprobe analysis, and IR and UV/VIS single-crystal spectroscopy. The IR spectra of the different samples commonly show a main intense OH À stretching band located at 3563 cm À1 , but other OH À bands can sometimes be observed as well. Structural OH À concentrations, calculated from the IR spectra, vary from about 0.006 to 0.240 wt% H 2 O. The UV/VIS spectra indicate that there can be slight, but not fully understood, differences in the electronic state between synthetic and natural andradite crystals. The C p behavior was determined by relaxation calorimetry between 2 and 300 K and by differential scanning calorimetry (DSC) methods between 150/300 and 700/950 K, employing the same andradite samples that were used for the other characterization measurements. The low-temperature C p results show a magnetic phase transition with a Néel temperature of 11.3 ± 0.2 K, which could be slightly affected by the precise electronic state of Fe 2þ/3þ in the crystals. The published adiabatic calorimetry results on andradite do not provide a full and correct thermal description of this magnetic transition. The calorimetric C p measurements give a best estimate for the standard third-law entropy at 298.15 K for andradite of S o ≈ 324 ± 2 J/mol · K vs. the value of 316.4 ± 2.0 J/mol · K, as given in an early adiabatic investigation. Both natural and synthetic crystals give similar S o values within experimental uncertainty of about 1.0%, but one natural andradite, richer in OH, may have a very slightly higher value around S o ≈ 326 J/mol · K. Low-temperature DSC measurements made below 298 K agree excellently with those from relaxation calorimetry. The DSC measurements above 298 K show a similarity in C p behavior among natural and synthetic andradites. A C p polynomial for use above room temperature to approximately 1000 K was calculated from the data on synthetic andradite giving: C p (J/mol · K) = 599.09 (±14) À 2709.5 (±480) · T À0.5 À 1.3866 (±0.26) · 10 7 · T À2 þ 1.6052 (±0.42) · 10 9 · T À3 .

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The Profile of Trace Elements, Including the Ree, in Gem-Quality Green Andradite From Classic Localities

Cited by 17 publications

References 25 publications

Gem-Quality Green Cr-Bearing Andradite (var. Demantoid) from Dobšiná, Slovakia

Gem-Quality Green Cr-Bearing Andradite (var. Demantoid) from Dobšiná, Slovakia

Garnets from Val d’Ala Rodingites, Piedmont, Italy: An Investigation of Their Gemological, Spectroscopic and Crystal Chemical Properties

Heat capacity and entropy behavior of andradite: a multi-sample and −methodological investigation

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