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Beryl. Aqua marine. Heliodor. Morganite. Emerald. Goshenite. Beryl. The varieties of beryl. Beryl: golden or red variety. Emerald: green variety. Aquamarine: blue variety. Morganite: pink variety . Heliodor: greenish-yellow variety. Goshenite: colourless variety.
BerylAqua marineHeliodorMorganiteEmeraldGosheniteBerylThe varieties of berylBeryl: golden or red varietyEmerald: green varietyAquamarine: blue varietyMorganite: pink variety Heliodor: greenish-yellow varietyGoshenite: colourless variety- Emeralds were mined in ancient Egypt 4000 years agoInteresting history:- In the 1600’s, high quality emerald reached Europe.- The Spaniards seized the emeralds from the Pre-Colombian people.- Mining in Colombia is still going on today, and often associated with criminal activities.The physical properties of berylGroup: beryl is a cyclosilicate Luster: vitreous, transparent to translucent Cleavage: imperfect in one direction, conchoidal fractureHardness: 7.5 - 8Specific gravity: 2.6 – 2.9 on averageCrystal habit: hexagonal prism with pincoid terminationThe chemical properties of berylBeryl is a beryllium aluminum silicate Be3Al2(Si6O18) BeO: 14.0%Composition:Al2O3: 19.0%SiO2: 67.0%The vertical hexagonal channels, which are normally vacant, can be occupied by alkali elements such as Li, Na, and Rb or neutral molecules such as H2O or CO2.This image shows the hexagonal structure along the c-axis of berylSilica tetrahedra (upper layer)Silica tetrahedra (lower layer)Beryllium tetrahedraAluminum polyhedronSimilar but rare species include Euclase [BeAl(SiO4)(OH)] and gadolinite [YFe2+Be2(SiO4)2O2] cabThe crystallographic properties of berylCrystal system: hexagonalPoint Group: 6/m 2/m 2/mUnit cell parameters:a = 9.23 Åc = 9.19ÅZ = 2Space group: P6/mccBeryl tetrahedronAluminum polyhedronSilicon tetrahedronOxygen atombacThe crystallographic properties of berylBeryl tetrahedronAluminum polyhedronSilicon tetrahedronOxygen atomCrystallographic data of berylSource: Morosin (1972)The optical properties of berylBeryl is uniaxial negative (oblate indicatrix) = 1.560 – 1.602 = 1.557 – 1.599 = 0.045 (3rd order interference colors)Weak to distinct pleochroismMay be zonedMay be twinneda axisc axisThe thermodynamic properties of berylOpen circles are for berylClosed circles are for emeraldBoth crystals exhibit a negative thermal expansion along the c axisSource: Morosin (1972)Igneous rocksMetamorphic rocksOccurrences of BerylIn granite, granite pegmatite, rarely in nepheline syeniteIn low to high temperature hydrothermal veinsAssociated minerals include micas, quartz, euclase, calcite, tourmaline, lepidote, spodumene, cassiterite topaz, and feldsparsLocations on Earth:Colombia, Brazil, Madagascar, Zimbabwe, Pakistan, Afghanistan, Russia, United States (Ca, Co, Id, Ut, NC)
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