DOCSLIB.ORG

Environmental Effects on the Fracture of Oxide Ceramics

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Environmental Effects on the Fracture of Oxide Ceramics UITNODIGING U bent van harte welkom bij de openbare Environmental Environmental effects on the fracture of oxide ceramics verdeding van mijn Environmental effects proefschrift Environmental on the fracture of oxide ceramics effects on the fracture of oxide ceramics De promotieplechtigheid zal plaatshebben op woensdag 18 december 2002 om 16.00 uur in het Auditorium van de Technische Universiteit Eindhoven. Aansluitend aan deze plechtigheid zal een receptie plaatsvinden waarvoor U ook van harte bent uitgenodigd. Niels van der Laag Niels van der Laag Niels van der Laag F.D. Rooseveltlaan 239 5625 AZ Eindhoven 040-2486540 [email protected] ± 170 pag. = 11mm rug f.c. glanslaminaat Environmental effects on the fracture of oxide ceramics PROEFSCHRIFT ter verkrijging van de graad van doctor aan de Technische Universiteit Eindhoven, op gezag van de Rector Magnificus, prof.dr. R.A. van Santen, voor een commissie aangewezen door het College voor Promoties in het openbaar te verdedigen op woensdag 18 december 2002 om 16.00 uur door Niels Johan van der Laag geboren te Boxmeer Dit proefschrift is goedgekeurd door de promotoren: prof.dr. G. de With en prof.dr. R.C. Bradt Copromotor: dr.ir. L.J.M.G. Dortmans Druk: Universiteitsdrukkerij, Technische Universiteit Eindhoven CIP-DATA LIBRARY TECHNISCHE UNIVERSITEIT EINDHOVEN Laag, Niels J. van der Environmental effects on the fracture of oxide ceramics / by Niels J. van der Laag. Eindhoven : Technische Universiteit Eindhoven, 2002. Proefschrift. ISBN 90-386-2754-8 NUR 913 Trefwoorden: keramische materialen; breuk / vastestofchemie / spinel; magnesium aluminaat / gahniet / zink aluminaat / breukmechanica / fysisch-chemische simulatie en modellering; thermische eigenschappen Subject headings: ceramics; fracture / solid state chemistry / spinel; magnesium aluminate / gahnite / zinc aluminate / fracture mechanics / physicochemical simulation and modeling; thermal properties Aan mijn ouders Table of Contents 1 Introduction . 1 1.1 Galloping Gertie. 1 1.2 Ceramics and failure. 2 1.3 Aim and lay-out of this thesis. 3 1.4 References . 6 2 Theoretical and computational background . 7 2.1 Introduction . 7 2.2 Fracture mechanics: Stress intensity approach. 8 2.2.1 Stress concentrators 2.2.2 Stress intensity factor 2.3 Fracture mechanics: Energy approach . 11 2.3.1 Griffith energy balance 2.3.2 Mechanical energy release rate 2.3.3 Intrinsic work of fracture 2.3.4 Failure criterion 2.4 Adsorption . 15 2.4.1 Adsorption isotherm 2.4.2 Adsorption and fracture energy 2.4.3 Adsorption and fracture toughness 2.5 Subcritical crack growth. 18 2.5.1 General 2.5.2 Constitutive model 2.5.3 Empirical power law 2.5.4 Combined kinetic and adsorption model v Table of contents 2.6 Experimental mechanical tests . 23 2.6.1 Fracture toughness: SENB 2.6.2 Effect SCG in SENB test 2.6.3 Strength: Three-point bending 2.6.4 Fracture toughness - strength ratio 2.7 Computer simulations. 28 2.7.1 General 2.7.2 Bulk and surface properties 2.7.3 Potentials 2.7.3.1 Pair potentials (PP) 2.7.3.2 Density Functional Theory 2.8 References . 33 3 Water vapour influence on the fracture of commercially applied oxide ceramics. 35 3.1 Introduction . 35 3.2 Experimental . 36 3.2.1 Materials and specimens 3.2.2 Fracture toughness and strength 3.2.3 Measurement 3.3 Results and discussion . 39 3.3.1 Fractography 3.3.2 Fracture toughness 3.3.3 Relation between fracture strength and fracture toughness for Wesgo995 3.4 Conclusions . 47 3.5 Acknowledgements . 48 3.6 References . 49 4 Subcritical crack growth in calcium hydroxyapatite . 51 4.1 Introduction . 51 4.2 Experimental . 53 4.2.1 Synthesis 4.2.2 Characterisation 4.2.3 Fracture 4.3 Results and discussion . 54 4.3.1 Synthesis and characterisation 4.3.2 Fractography 4.3.3 Fracture toughness 4.3.4 Analysis vi Table of contents 4.4 Conclusions . 60 4.5 Acknowledgements . 61 4.6 References . 61 5 Fracture of magnesium aluminate spinel (MgAl2O4) . 63 5.1 Introduction . 63 5.2 Experimental . 65 5.2.1 Material preparation and characterisation 5.2.2 Mechanical testing 5.2.3 Surface investigation preparation 5.3 Results and discussion of bulk properties . 68 5.3.1 Characterisation 5.3.2 Mechanical characterisation 5.4 Results and discussion of surface properties . 73 5.4.1 EBSD 5.4.2 LEIS 5.4.3 DRIFTS 5.5 Conclusions . 79 5.6 Appendix: Fracture and EBSD. 80 5.7 Acknowledgements . 81 5.8 References . 82 6 Structural, mechanical, thermophysical and dielectric properties of zinc aluminate (ZnAl2O4) . 85 6.1 Introduction . 85 6.2 Crystallographic aspects of zinc aluminate . 86 6.3 Instrumentation. 87 6.4 Preparation . 88 6.4.1 Powder synthesis 6.4.2 Compaction and sintering 6.5 Results and discussion . 89 6.5.1 Structural properties 6.5.1.1 XRD 6.5.1.2 Composition 6.5.1.3 MAS-NMR 6.5.2 Mechanical properties vii Table of contents 6.5.3 Thermophysical properties 6.5.3.1 Heat capacity 6.5.3.2 Thermal diffusivity 6.5.3.3 Thermal conductivity 6.5.4 Dielectric properties 6.6 Conclusions . 100 6.7 Acknowledgements . 101 6.8 References . 101 7 Computational investigation of bulk and surface properties of zinc aluminate (ZnAl2O4) . 105 7.1 Introduction . 105 7.2 Experimental . 106 7.3 Computational methods . 106 7.3.1 Potentials 7.3.2 Surface energy 7.4 Results and discussion . 108 7.4.1 Structural and bulk properties 7.4.2 Surfaces (simulation) 7.4.3 Surfaces (experimental) 7.5 Conclusions . 115 7.6 Acknowledgements . 116 7.7 References . 116 8 Predictive calculation of intrinsic thermophysical properties from ab-initio phonon density of states: a case study for oxide ceramics . 119 8.1 Introduction . 119 8.2 Theory . 120 8.2.1 Phonons 8.2.2 Thermophysical properties 8.2.3 Debye model 8.2.4 Moment representation of phonon density of states 8.3 Criteria for comparison . 124 8.4 Computer simulation . 125 viii Table of contents 8.5 Results and discussion . 125 8.5.1 Density of states 8.5.2 Heat capacity 8.5.3 Entropy 8.5.4 Debye temperature 8.5.5 Moments of density of states 8.5.6 Debye temperature from elastic constants 8.6 Conclusions . 131 8.7 Acknowledgements . 131 8.8 References . 132 9 Epilogue: overview, conclusions & future work . 133 9.1 Introduction . ..
Load more

Recommended publications
  • Symposium on Agate and Cryptocrystalline Quartz
    Symposium on Agate and Cryptocrystalline Quartz September 10 – 13, 2005 Golden, Colorado Sponsored by Friends of Mineralogy, Colorado Chapter; Colorado School of Mines Geology Museum; and U.S. Geological Survey 2 Cover Photos {top left} Fortification agate, Hinsdale County, Colorado, collection of the Geology Museum, Colorado School of Mines. Coloration of alternating concentric bands is due to infiltration of Fe with groundwater into the porous chalcedony layers, leaving the impermeable chalcedony bands uncolored (white): ground water was introduced via the symmetric fractures, evidenced by darker brown hues along the orthogonal lines. Specimen about 4 inches across; photo Dan Kile. {lower left} Photomicrograph showing, in crossed-polarized light, a rhyolite thunder egg shell (lower left) a fibrous phase of silica, opal-CTLS (appearing as a layer of tan fibers bordering the rhyolite cavity wall), and spherulitic and radiating fibrous forms of chalcedony. Field of view approximately 4.8 mm high; photo Dan Kile. {center right} Photomicrograph of the same field of view, but with a 1 λ (first-order red) waveplate inserted to illustrate the length-fast nature of the chalcedony (yellow-orange) and the length-slow character of the opal CTLS (blue). Field of view about 4.8 mm high; photo Dan Kile. Copyright of articles and photographs is retained by authors and Friends of Mineralogy, Colorado Chapter; reproduction by electronic or other means without permission is prohibited 3 Symposium on Agate and Cryptocrystalline Quartz Program and Abstracts September 10 – 13, 2005 Editors Daniel Kile Thomas Michalski Peter Modreski Held at Green Center, Colorado School of Mines Golden, Colorado Sponsored by Friends of Mineralogy, Colorado Chapter Colorado School of Mines Geology Museum U.S.
    [Show full text]
  • Compilation of Reported Sapphire Occurrences in Montana
    Report of Investigation 23 Compilation of Reported Sapphire Occurrences in Montana Richard B. Berg 2015 Cover photo by Richard Berg. Sapphires (very pale green and colorless) concentrated by panning. The small red grains are garnets, commonly found with sapphires in western Montana, and the black sand is mainly magnetite. Compilation of Reported Sapphire Occurrences, RI 23 Compilation of Reported Sapphire Occurrences in Montana Richard B. Berg Montana Bureau of Mines and Geology MBMG Report of Investigation 23 2015 i Compilation of Reported Sapphire Occurrences, RI 23 TABLE OF CONTENTS Introduction ............................................................................................................................1 Descriptions of Occurrences ..................................................................................................7 Selected Bibliography of Articles on Montana Sapphires ................................................... 75 General Montana ............................................................................................................75 Yogo ................................................................................................................................ 75 Southwestern Montana Alluvial Deposits........................................................................ 76 Specifi cally Rock Creek sapphire district ........................................................................ 76 Specifi cally Dry Cottonwood Creek deposit and the Butte area ....................................
    [Show full text]
  • On Palaeozoic–Mesozoic Brittle Normal Faults Along the SW Barents Sea Margin: Fault Processes and Implications for Basement Permeability and Margin Evolution
    research-articleResearch ArticleXXX10.1144/jgs2014-018K. Indrevær et al.Brittle Faults on the SW Barents Sea Margin 2014 Downloaded from http://jgs.lyellcollection.org/ by guest on October 9, 2021 Journal of the Geological Society, London. http://dx.doi.org/10.1144/jgs2014-018 Published Online First © 2014 The Authors On Palaeozoic–Mesozoic brittle normal faults along the SW Barents Sea margin: fault processes and implications for basement permeability and margin evolution KJETIL INDREVÆR1,2*, HOLGER STUNITZ1 & STEFFEN G. BERGH1 1Department of Geology, University of Tromsø, N-9037 Tromsø, Norway 2DONG E&P Norge AS, Roald Amundsens Plass 1, N-9257 Tromsø, Norway *Corresponding author (e-mail: [email protected]) Abstract: Palaeozoic–Mesozoic brittle normal faults onshore along the SW Barents Sea passive margin off northern Norway give valuable insight into fault and fluid flow processes from the lower brittle crust. Micro- structural evidence suggests that Late Permian–Early Triassic faulting took place during multiple phases, with initial fault movement at minimum P–T conditions of c. 300 °C and c. 240 MPa (c. 10 km depth), followed by later fault movement at minimum P–T conditions of c. 275 °C and c. 220 MPa (c. 8.5 km depth). The study shows that pore pressures locally reached lithostatic levels (240 MPa) during faulting and that faulting came to a halt during early (deep) stages of rifting along the margin. Fault permeability has been controlled by heal- ing and precipitation processes through time, which have sealed off the core zone and eventually the damage zones after faulting. A minimum average exhumation rate of c.
    [Show full text]
  • Non-Stoichiometric Magnesium Aluminate Spinel
    NON-STOICHIOMETRIC MAGNESIUM ALUMINATE SPINEL: MICROSTRUCTURE EVOLUTION AND ITS EFFECT ON PROPERTIES by J. Aaron Miller A thesis submitted to the Faculty and the Board of Trustees of the Colorado School of Mines in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Materials Science). Golden, Colorado Date _________________________ Signed: __________________________________ J. Aaron Miller Signed: __________________________________ Ivar E. Reimanis Thesis Advisor Golden, Colorado Date _________________________ Signed: _________________________ Dr. Angus Rockett Professor and Head Department of Metallurgical and Materials Engineering ii ABSTRACT Magnesium aluminate spinel is a material of interest for transparent armor applications. Owing to its unique combination of transparency to large portions of the electromagnetic spectrum and mechanical robustness, spinel is among the front runners for applications including transparent armor windows for military vehicles and space craft windows, missile radomes, and infrared windows. However, failure in such applications may lead to severe outcomes, creating motivation to further improve the mechanical reliability of the materials used. In this thesis, potential toughening mechanisms that utilize unique control over the evolution of second phase particles are explored. Al-rich spinel (MgO•nAl2O3) with a composition of n = 2 is investigated. First, it is demonstrated that precipitation of second phase Al2O3 from single phase spinel can be achieved by modifying the densification
    [Show full text]
  • Methods Used to Identifying Minerals
    METHODS USED TO IDENTIFYING MINERALS More than 4,000 minerals are known to man, and they are identified by their physical and chemical properties. The physical properties of minerals are determined by the atomic structure and crystal chemistry of the minerals. The most common physical properties are crystal form, color, hardness, cleavage, and specific gravity. CRYSTALS One of the best ways to identify a mineral is by examining its crystal form (external shape). A crystal is defined as a homogenous solid possessing a three-dimensional internal order defined by the lattice structure. Crystals developed under favorable conditions often exhibit characteristic geometric forms (which are outward expressions of the internal arrangements of atoms), crystal class, and cleavage. Large, well- developed crystals are not common because of unfavorable growth conditions, but small crystals recognizable with a hand lens or microscope are common. Minerals that show no external crystal form but possess an internal crystalline structure are said to be massive. A few minerals, such as limonite and opal, have no orderly arrangement of atoms and are said to be amorphous. Crystals are divided into six major classes based on their geometric form: isometric, tetragonal, hexagonal, orthorhombic, monoclinic, and triclinic. The hexagonal system also has a rhombohedral subdivision, which applies mainly to carbonates. CLEAVAGE AND FRACTURE After minerals are formed, they have a tendency to split or break along definite planes of weakness. This property is called cleavage. These planes of weakness are closely related to the internal structure of the mineral, and are usually, but not always, parallel to crystal faces or possible crystal faces.
    [Show full text]
  • An Examination of Red Beryl
    An Examination of Red Beryl By FRANK MILEY Graduate Gemologist Los Alamos, New Mexico Introduction sions. The largest faceted red beryl that has been reported 3 is 2.93 ct. Red beryl is a gem that has recently The author has not had the oppor- been coming into prominence. Where tunity to see or examine this rare does it come from? How much is gemstone. available? What does it look like? In some literature red beryl is listed How can it be identified? Recent as bixbite. If you should do a litera- acquisition of a faceted gem prompted ture survey, you should be aware of these questions. After researching both names. In this article it is re- available literature and finding very ferred to as red beryl. little gemological information, it be- came obvious that some personal re- Properties search was to be done on as much red Several faceted specimens of the beryl as could be examined. Utah material were examined for this report. New Mexico material was on Sources display- as crystal specimens; it was Red beryl is only found in three much too small to be faceted. This locations in the United States. No material was not available for micro- other sources have been reported. It scopic examination. It was noted occurs in the Thomas and Wah-Wah however, that the tone and hue were Mountain ranges in Utah I and in the very close to that of the Thomas Black Range in New Mexico 2. All Mountain material. The Utah mater- crystals are small; the largest crystals ial exhibited differences in transpar- are found in Utah.
    [Show full text]
  • Beryl Be3al2si6o18 C 2001 Mineral Data Publishing, Version 1.2 ° Crystal Data: Hexagonal
    Beryl Be3Al2Si6O18 c 2001 Mineral Data Publishing, version 1.2 ° Crystal Data: Hexagonal. Point Group: 6=m 2=m 2=m: Crystals prismatic to tabular, with 1010 , 0001 , and 1120 ; may be complexly terminated by pyramids, to 18 m and 180 t. Also rfadial,gtrfapichge, columf nar;ggranular to compact. Twinning: On hkil forms, rarely. f g Physical Properties: Cleavage: Imperfect on 0001 . Fracture: Conchoidal to uneven. Tenacity: Brittle. Hardness = 7.5{8 VHN = 119f0{145g0, 1300 average. D(meas.) = 2.63{2.97 increasing with alkali content; 2.7 average. D(calc.) = 2.640 Optical Properties: Transparent to translucent. Color: Colorless, white, pale blue to sky-blue, bluish green through green to greenish yellow or yellow, rose to peach, deep pink to raspberry-red; may be zoned; commonly colorless in thin section. Streak: White. Luster: Vitreous, resinous. Optical Class: Uniaxial ({). Pleochroism: Weak to distinct; O = colorless, yellowish green, light blue, yellowish red; E = sea-green, blue, purplish red. ! = 1.567{1.610 ² = 1.565{1.599; increasing with alkali content. Cell Data: Space Group: P 6=mcc: a = 9.205{9.274 c = 9.187{9.249 Z = 2 X-ray Powder Pattern: Royalston, Massachusetts, USA. 2.867 (100), 3.254 (95), 7.98 (90), 4.60 (50), 3.99 (45), 3.015 (35), 2.523 (30) Chemistry: (1) (2) (3) (1) (2) (3) SiO2 65.59 63.29 67.07 Na2O 0.26 1.23 Al2O3 18.25 17.76 18.97 Cs2O 3.79 FeO 1.16 Rb2O 0.05 BeO 13.46 10.79 13.96 LOI 0.70 1.10 Li2O 1.30 Total 99.42 99.31 100.00 (1) Mursinka, Russia; by electron microprobe.
    [Show full text]
  • The Element Six Cvd Diamond Handbook
    THE ELEMENT SIX CVD DIAMOND HANDBOOK Contact Element Six Technologies at [email protected] CONTENTS INTRODUCING DIAMOND 3 PHYSICAL PROPERTIES 4 DIAMOND CLASSIFICATION 5 DIAMOND SYNTHESIS 6 TYPES OF CVD DIAMOND 7 CRYSTALLOGRAPHY 8 MECHANICAL STRENGTH 9 POLISHING OF DIAMOND 10 DIAMOND SURFACES 11 PROPERTIES OPTICAL PROPERTIES 12 OPTICAL CONSTANTS 13 RAMAN SCATTERING 14 SINGLE CRYSTAL OPTICS 15 POLYCRYSTALLINE OPTICS 16 EMISSIVITY AND RF WINDOWS 17 PRECISION COMPONENTS 18 Advances in the synthesis and processing THERMAL PROPERTIES 19 technology for CVD diamond has resulted ELECTRONIC PROPERTIES 20 in materials with exceptional diamond properties in practical components. ELECTROCHEMICAL PROPERTIES 21 Engineered single crystal CVD diamond, with ultra low absorption and birefringence DATASHEETS combined with long optical path lengths, ELECTRONIC GRADES 22 has made Monolithic Diamond Raman OPTICAL AND RF GRADES 23 Lasers a practical reality. MECHANICAL GRADES 24 THERMAL GRADES 25 ELECTROCHEMICAL GRADE 26 FURTHER READING 27 The Element Six CVD Diamond Handbook 2 INTRODUCING DIAMOND Diamond is characterised by its exceptional hardness, robustness and its optical and thermal properties; pre-eminent as a gemstone and an industrial tool. Natural diamond has an inherent variability and scarcity that limits its use in engineering applications. Developments in synthesis processes have enabled the production of consistently engineered synthetic diamond; firstly in the 1950s using high pressure and high temperature and later using chemical vapour deposition in the 1980s to produce the IT IS ALL IN THE STRUCTURE exceptional covalent crystal diamond. Diamond’s properties derive from its The modern industrial world consumes structure; tetrahedral covalent bonds approximately 800 tonnes of synthetic between its four nearest neighbours, diamond, around 150 times the amount of linked in a cubic lattice.
    [Show full text]
  • Agate Recrystallisation: Evidence from Samples Found in Archaean and Proterozoic Host Rocks, Western Australia
    Australian Journal of Earth Sciences (2006) 53, (235 – 248) Agate recrystallisation: evidence from samples found in Archaean and Proterozoic host rocks, Western Australia T. MOXON1*, D. R. NELSON2 AND M. ZHANG3 155 Common Lane, Auckley, Doncaster DN9 3HX, UK. 2Department of Applied Physics, Curtin University of Technology, GPO Box U1987, Perth, WA 6001, Australia. 3Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK. The crystallite size and density of agates from three Western Australian host rocks aged 1.84, 2.72 and 3.48 Ga have been determined. Infrared and Raman spectra from these ancient agates have respectively shown minimal water and zero moganite content. Data comparison of agates from Western Australian and younger hosts showed an advanced crystallisation in the Western Australian samples with, in some instances, the crystallite size comparable to macrocrystalline quartz. Low-grade metamorphism is present in the host rocks and localised heating is one possible cause of the increased crystallite growth. Micrographs of one agate sample from the Warrawoona Group (3.48 Ga) show a breakdown in the fibrous chalcedony; regional variations within the agate were supported by data from infrared and X-ray diffraction. It has been shown that part of the sample had undergone a transformation of the fibrous chalcedony to granular microcrystalline quartz. The Crystallinity Index for microcrystalline quartz, based upon the degree of resolution of the (212) quartz reflection, offers a rapid method to identify abnormal crystallite growth that could serve as a palaeoindicator of host-rock metamorphism. KEY WORDS: agate, Archaean, Crystallinity Index, infrared, moganite, Raman spectroscopy, recrys- tallisation, water, X-ray diffraction.
    [Show full text]
  • Properties of Minerals I. Crystal Habits II. Cleavage and Fracture in Minerals
    Please be careful with samples. You can do just about anything you want to the grungy ones, but be nice to the pretty specimens as they are irreplaceable. Properties of Minerals Name__________________________________ I. Crystal Habits Not all mineralogical samples form nicely shaped crystals, but when they do, the shape can be helpful in identifying the mineral. The habit of a crystal refers to its shape. (But, it refers only to the shape that the crystal forms as it grows, not as it breaks--see next section of cleavage and fracture.) For example, some minerals such as halite tend to be cubic, while others such as the micas are foliated and tend to form sheets or books. A large number of terms are used to describe habit; they are summarized in your mineralogy text (Table 3.2). Some of the most commonly used terms that you should be familiar with are: bladed equant blocky tabular columnar foliated micaceous sheety fibrous dendritic granular massive concentric prismatic cubic hexagonal octahedral orthorhombic Make up your own terms if you want to, just as long as they have a clear meaning (e.g., "grape-like"). II. Cleavage and Fracture in Minerals Cleavage, parting and fracture refer to the ways a mineral breaks when an external force is applied. Since minerals have atomic structures that are not the same in all directions, there are some preferred directions and methods of breaking. Cleavage is the tendency of minerals to break along one or more sets of parallel planes. In some minerals, such as micas, it is nearly perfect in one direction.
    [Show full text]
  • Beryl the Varieties of Beryl the Physical Properties of Beryl
    Beryl Beryl Aqua marine Heliodor Morganite Emerald Goshenite 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 Interesting history: - Emeralds were mined in ancient Egypt 4000 years ago - 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 beryl Group: beryl is a cyclosilicate Luster: vitreous, transparent to translucent Cleavage: imperfect in one direction, conchoidal fracture Hardness: 7.5 - 8 Specific gravity: 2.6 – 2.9 on average Crystal habit: hexagonal prism with pincoid termination 1 The chemical properties of beryl Beryl is a beryllium aluminum silicate Be3Al2(Si 6O18) Composition: BeO: 14.0% 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 H 2O or CO2. This image shows the hexagonal structure along the c-axis of beryl Silica tetrahedra (upper layer) Silica tetrahedra (lower layer) Beryllium tetrahedra Aluminum polyhedron Similar but rare species include Euclase [BeAl(SiO4)(OH)] and 2+ gadolinite [YFe Be2(SiO4) 2O 2] The crystallographic properties of beryl Crystal system: hexagonal Point Group: 6/m 2/m 2/m Unit cell parameters: a = 9.23 Å c = 9.19Å Z = 2 Space group: P6/mcc c a b Beryl
    [Show full text]
  • Prospecting for and Instructions on How to Finish Fire Agate Gems
    Prospecting For And Instructions On How To Finish Fire Agate Gems In this booklet I will do my best to help the lapidarian who wants to start working with Fire Agates as well as those who only need a little help on just how to get started. In turn I will do all that I can to encourage the reader who is not a lapidarian to be able to start a lifetime hobby of it. I will also include as much information as I can possibly find on the subject through researching current books. It has been said that knowledge is wealth. I have found that wealth is not found in monetary means alone. To me happiness is the ultimate wealth. Even if you never do work with rocks, it is nice to learn as we go through life. Who knows it could spark that tad bit of interest that would start you on the road to being a true rock hound for life. In turn be able to share the beautiful world of lapidary with millions of rock hound people around the world, who I feel in my world are among the finest people I have ever had the pleasure of knowing. Sometimes in life it is just that little spark that sets off the interest in your mind that in some way will change your thinking for the remainder of your life. I wish that every child had the opportunity to go out with their parents hunting rocks together and finding the things that set us apart from the other animals on our planet.
    [Show full text]