Eraser Cleaning of Gypsum Plaster

Total Page:16

File Type:pdf, Size:1020Kb

Eraser Cleaning of Gypsum Plaster Article: Eraser cleaning of gypsum plaster: Evaluating damage potential using reflectance transformation imaging Author(s): Kathryn Brugioni Source: Objects Specialty Group Postprints, Volume Twenty-Two, 2015 Pages: 205-224 Editors: Emily Hamilton and Kari Dodson, with Sarah Barack and Kate Moomaw, Program Chairs ISSN (print version) 2169-379X ISSN (online version) 2169-1290 © 2016 by The American Institute for Conservation of Historic & Artistic Works 1156 15th Street NW, Suite 320, Washington, DC 20005 (202) 452-9545 www.conservation-us.org Objects Specialty Group Postprints is published annually by the Objects Specialty Group (OSG) of the American Institute for Conservation of Historic & Artistic Works (AIC). It is a conference proceedings volume consisting of papers presented in the OSG sessions at AIC Annual Meetings. Under a licensing agreement, individual authors retain copyright to their work and extend publications rights to the American Institute for Conservation. This article is published in the Objects Specialty Group Postprints, Volume Twenty-Two, 2015. It has been edited for clarity and content. The article was peer-reviewed by content area specialists and was revised based on this anonymous review. Responsibility for the methods and materials described herein, however, rests solely with the author(s), whose article should not be considered an official statement of the OSG or the AIC. ERASER CLEANING OF GYPSUM PLASTER: EVALUATING DAMAGE POTENTIAL USING REFLECTANCE TRANSFORMATION IMAGING KATHRYN BRUGIONI Practically all methods for dry-cleaning gypsum plaster involve abrasion on some scale. Previous studies of abrasion-cleaning methods have successfully quantified damage potential by imaging test coupons in a scanning electron microscope; however, this instrumentation is not available to everyone. Furthermore, the photomicrographs used show a level of detail that will never be perceptible to the human eye. In the absence of scanning electron microscope analysis, a more accessible method for measuring surface abrasion should be assayed: reflectance transformation imaging. This study explores the extent to which reflectance transformation imaging can reveal these surface changes to gypsum plaster caused by multiple dry-cleaning materials. Reflectance transformation imaging captures were compared to scanning electron microscope photomicrographs, which allowed for a calibration of the data collected with reflectance transformation imaging. KEYWORDS: Gypsum plaster, Dry-cleaning, Eraser cleaning, Reflectance Transformation Imaging 1. INTRODUCTION Being moldable, carvable, and paintable, gypsum plaster has been used since the beginning of human history. For all of plaster’s versatility and stability, the surfaces of artifacts made thereof can become embedded with dust and grime. A porous material that is often of a uniform color, plaster is one of the most difficult materials to clean successfully without solubilizing the substrate, without creating tide lines, without driving soiling into its pores, and without abrading the surface. To avoid the problems associated with introducing liquids into a plaster-cleaning system, erasers are often employed to dry-surface-clean such objects. After a discussion of the material terminology and principles involved, this article will describe the various precedents in eraser cleaning and the application of this technique to plaster. The use of reflectance transformation imaging (RTI) to evaluate damage potential of such treatments will then be considered in comparison to less accessible methods, such as SEM. The research presented at the 2015 OSG Tips Session was undertaken in conjunction with a gypsum-plaster treatment, performed at the Conservation Center of the Institute of Fine Arts, New York University, for which an eraser cleaning was indicated. The treatment of this object was employed as proof of concept of the preceding research. 1.1 TERMINOLOGY Any cleaning method must be designed with the nature of the material in mind; however, there is often confusion over the definition of the word plaster. In certain contexts, its meaning depends on material function, whereas in others, its meaning depends on its chemistry. Many discipline-specific lexicons, such as the Getty Research Institute’s Art and Architecture Thesaurus Online (Plaster 2004; Stucco 2004) and the Museum of Fine Arts Boston’s CAMEO (Plaster 2013; Stucco 2013), tend to define plaster and stucco differently in relation to the more chemically specific terms,lime plaster and gypsum plaster. As such, conflations of such terms commonly occur. Although this study was borne of the study and treatment of a gypsum plaster object, the following procedures and findings could be applied to materials of comparable porosity and hardness. AIC Objects Specialty Group Postprints, Vol. 22, 2015 205 13_Brugioni.indd 205 24/01/2017 12:58 206 1.2 CHEMISTRY AND STRUCTURE OF GYPSUM PLASTER Gypsum plaster is mined as the mineral gypsum, calcium sulfate dihydrate (CaSO4 · 2H2O). After mining, it is ground, purified, and calcined. This process typically forms the “plaster” product, calcium sulfate hemihydrate (CaSO4 · ½ H2O), which when mixed with water reforms the dihydrate. The free water (the water in excess of the waters of hydration) evaporates after application or molding of the paste, leaving a hard, carvable, and paintable material, which is reusable if refired. The most common crystal forms are alpha and beta forms, the former being more acicular and prismatic, and the latter being tabular (Christensen, Jensen, and Nonat 2010). Different manufacturing processes create different polymorphs or different ratios thereof, and these crystal structures impart different properties on the final product (Singh and Middendorf 2007). Alpha-type crystals pack more tightly, forming a less porous, harder, heavier, and less-compressible material that is preferred for sculpture and for detailed mold making. Beta-type crystals form a lighter, more porous, less-durable plaster, favored for certain construction applications (Kogel et al. 2006). Various additives, including driers, retardants, accelerants, thickeners, plasticizers, and deflocculants, may be used to modify the microstructure of the hardened gypsum; reduce or increase its compressive strength; or modify curing time, density, compressibility, and porosity (Hummel et al. 2003; Singh and Middendorf 2007; Guan et al. 2010). More than one plaster type may be present on the same object in the form of repairs, revisions, or where different plaster properties are needed. Accordingly, cleaning results may vary between different objects or across one surface. 2. PRECEDENTS IN ERASER CLEANING No matter the formulation of the material used, pores form in cast plaster due to the imperfect packing of crystals and the gradual evaporation of free water from the substrate. This porosity allows soiling—in the form of grease and dust—to become easily ingrained in and below the surface of the plaster (fig. 1). Gypsum plaster is also slightly soluble in water (approximately 2.4 g/L at 208C), and aqueous treatment of any soiling carries the risk of driving surface dirt farther into the substrate (American Chemical Society 2006) (fig. 2). Because of its porosity and water sensitivity, plaster is often dry-cleaned with erasers to clear soiling without irreversibly driving it into the pores of the plaster. It is essential, however, that the correct eraser product be chosen, as most plasters are deceptively soft and can be scratched by a fingernail. Popular in the realm of paper conservation (Pearlstein et al. 1982), eraser cleaning has been adapted for the cleaning of stone by Williams and Lauffenburger (1995). As with any treatment protocol, it is important to first ensure the suitability and stability of the materials used for treatment and then to evaluate their damage potential both physically and chemically. Pearlstein et al. (1982) and Williams and Lauffenburger (1995) juxtaposed three primary types of erasers: those based on rubber (containing rubber, drying oils, sulfur, and abrasives), factice (containing vulcanized vegetable or animal oils cross-linked with sulfur bonds), and vinyl (usually containing polyvinyl chloride, phthalate plasticizer, and calcium carbonate) (AIC, Book and Paper Group 1992). These studies consider the chemical composition of the various eraser types, their degradation products, their working properties, their efficacy in treatment, and their mechanical damage potential. Although such products should be periodically reevaluated to account for any changes in formulation, the findings detailed in the preceding references provide a point of departure for future testing. In brief, these studies caution against the use of products based on factice and rubber, as they leave considerable amounts of residue, and this residue then degrades to sulfurous by-products on treated surfaces. These evaluations also establish the importance of screening erasers for the presence of abrasives, which are included to increase grating action, and colorants, which can leave surface streaks. These ingredients are not appropriate in the context of a conservation treatment. Brugioni AIC Objects Specialty Group Postprints, Vol. 22, 2015 13_Brugioni.indd 206 24/01/2017 12:58 207 Fig. 1. Soiling, in the form of grease and dust, can become embedded in the porous plaster surface, causing considerable disfigurement. (Courtesy of Badde 2009, 26; Library Company of Philadelphia 2014) Fig. 2. UV photograph
Recommended publications
  • ENVIRONMENTAL RISK ASSESSMENT for GYPSUM TELLS POSITIVE STORY by Karen Bernick
    CCPs in Agriculture ENVIRONMENTAL RISK ASSESSMENT FOR GYPSUM TELLS POSITIVE STORY By Karen Bernick mending soils with !ue “…the risk assessment has shown that FGD gypsum gas desulfurization (FGD) contains extremely low concentrations of most trace gypsum o"ers a host of promising bene#ts to elements, about the same as found in mined gypsum agriculture, and this bene#cial use and, in most cases, lower than background soils.” providesA an opportunity for power plants to reduce disposal costs. lead and arsenic trouble spots; and other Chaney says the only risk he has iden- But is it safe? contaminant risks in plant uptake and food. tified occurs if livestock producers He is the lead USDA researcher on the FGD allow ruminants to eat large quanti- $e answer appears to be a resounding gypsum risk assessment. ties of stockpiled gypsum. “If livestock “yes” according to early reports from a producers prevent ruminants from eat- comprehensive risk assessment by the $e USDA-EPA assessment exam- ing gypsum by fencing in stockpiles, U.S. Department of Agriculture (USDA) ines what Chaney calls “new” FGD and limit grazing until after a rainfall to and U.S. Environmental Protection gypsum, a high quality form of syn- wash adhering FGD gypsum from for- Agency (EPA). $e assessment, likely thetic gypsum sought by agricultural age leaves, the sulfate risk is prevented,” to be concluded in 2013, addresses crop producers for its soil improvement he says. potential risks that land applications of bene#ts, calcium and sulfur supplies, FGD gypsum could pose to human health purity and relative low cost versus mined RISK ASSESSMENT or the environment.
    [Show full text]
  • Gypsum and Carbon Amendment's
    GYPSUM AND CARBON AMENDMENT’S INFLUENCE ON SOIL PROPERTIES, GREENHOUSE GAS EMISSIONS, GROWTH AND NUTRIENT UPTAKE OF RYEGRASS (Lolium perenne) DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Maninder Kaur Walia, M.S. Environment and Natural Resources Graduate Program The Ohio State University 2015 Dissertation Committee: Warren A. Dick, Advisor Rattan Lal Brian K. Slater Frederick C. Michel,Jr. Copyrighted by Maninder Kaur Walia 2015 Abstract Gypsum is a source of calcium and sulfur that improves the physical and chemical properties of the soil. With the benefits associated with gypsum use and the increased availability of synthetic gypsum, its application to soil in Ohio and the Midwest is increasing. Several studies have focused on the effect of gypsum on soil properties. However, little is known about how gypsum affects C stocks in soils. In this study, in addition to gypsum, we also treated the soil with glucose to create a high level of CO2 in the soil profile, and contrasted that with the more slowly released C from plant residues. The overall goal of this dissertation research was to evaluate the effect of plant residues, glucose and gypsum on the growth and nutrient uptake of ryegrass, chemical properties (including total and inorganic C stock) and physical properties of two contrasting soils in Ohio (Wooster silt loam and Hoytville clay loam). Specific objectives of this research were to quantify the effect of (1) gypsum and plant residues on greenhouse gas emissions, (2) gypsum and C amendments on quality of leachate water, (3) gypsum and C amendments addition on C fractions in soils, (4) gypsum, plant residues and glucose addition on soil fertility, growth and nutrients concentrations of ryegrass and (5) gypsum, glucose and plant residues on selected soil physical properties and aggregate-associated C and N.
    [Show full text]
  • “Mining” Water Ice on Mars an Assessment of ISRU Options in Support of Future Human Missions
    National Aeronautics and Space Administration “Mining” Water Ice on Mars An Assessment of ISRU Options in Support of Future Human Missions Stephen Hoffman, Alida Andrews, Kevin Watts July 2016 Agenda • Introduction • What kind of water ice are we talking about • Options for accessing the water ice • Drilling Options • “Mining” Options • EMC scenario and requirements • Recommendations and future work Acknowledgement • The authors of this report learned much during the process of researching the technologies and operations associated with drilling into icy deposits and extract water from those deposits. We would like to acknowledge the support and advice provided by the following individuals and their organizations: – Brian Glass, PhD, NASA Ames Research Center – Robert Haehnel, PhD, U.S. Army Corps of Engineers/Cold Regions Research and Engineering Laboratory – Patrick Haggerty, National Science Foundation/Geosciences/Polar Programs – Jennifer Mercer, PhD, National Science Foundation/Geosciences/Polar Programs – Frank Rack, PhD, University of Nebraska-Lincoln – Jason Weale, U.S. Army Corps of Engineers/Cold Regions Research and Engineering Laboratory Mining Water Ice on Mars INTRODUCTION Background • Addendum to M-WIP study, addressing one of the areas not fully covered in this report: accessing and mining water ice if it is present in certain glacier-like forms – The M-WIP report is available at http://mepag.nasa.gov/reports.cfm • The First Landing Site/Exploration Zone Workshop for Human Missions to Mars (October 2015) set the target
    [Show full text]
  • Moving Forwards
    Recycling Today Magazine ~> Moving Forward Page 1 of 3 recvdin MoVing Forward By: Timothy G. Townsend May 2003 URL: http:llwww.recyclingtoday,com/arficles/article.asp?lD=4759&CafiD=&SubCatlD= Gypsum drywall is a major component of modern buildings, yet it is often one of the least likely components of debris frem building construction, demolition or renovation to be recycled. Gypsum drywall typically makes up 5 percent to 25 percent of the weight of debris from building-related C&D activities, A typical rule of thumb for drywall generation from construction activities is one pound of drywall per cubic foot of construction. The amount of post-consumer drywall generated in Florida C&D debris in 2000 was estimated at nearly 500,000 tons. Most of this was disposed in unlined landfills. Recovery and recycling is always desired in place of lend- filling when feasible, but several environmentel factors (odor, groundwater contamination) create added incentive for recycling d~JwalL While several gypsum drywall recycling operations exist in North America at the current time, in many areas (Florida for example) drywa!l recycling is relatively nonexistent. This paper describe~ some of the issues facing the C&D debris industry and summarizes the current state of gypsum drywall recycling in North America. DRYWALL BASICS Gypsum drywall, often referred to as gypsum wallbeard or sheet rock, replaced gypsum piaster as the major interior wall surface because of its ease of installation and its fire resistant properties. Gypsum drywal! consists of approximately 90 percent gypsum and 10 percent paper facing and backing. Gypsum is a mineral composed of calcium sulfate (CaSOL and water (H20).
    [Show full text]
  • Historical Painting Techniques, Materials, and Studio Practice
    Historical Painting Techniques, Materials, and Studio Practice PUBLICATIONS COORDINATION: Dinah Berland EDITING & PRODUCTION COORDINATION: Corinne Lightweaver EDITORIAL CONSULTATION: Jo Hill COVER DESIGN: Jackie Gallagher-Lange PRODUCTION & PRINTING: Allen Press, Inc., Lawrence, Kansas SYMPOSIUM ORGANIZERS: Erma Hermens, Art History Institute of the University of Leiden Marja Peek, Central Research Laboratory for Objects of Art and Science, Amsterdam © 1995 by The J. Paul Getty Trust All rights reserved Printed in the United States of America ISBN 0-89236-322-3 The Getty Conservation Institute is committed to the preservation of cultural heritage worldwide. The Institute seeks to advance scientiRc knowledge and professional practice and to raise public awareness of conservation. Through research, training, documentation, exchange of information, and ReId projects, the Institute addresses issues related to the conservation of museum objects and archival collections, archaeological monuments and sites, and historic bUildings and cities. The Institute is an operating program of the J. Paul Getty Trust. COVER ILLUSTRATION Gherardo Cibo, "Colchico," folio 17r of Herbarium, ca. 1570. Courtesy of the British Library. FRONTISPIECE Detail from Jan Baptiste Collaert, Color Olivi, 1566-1628. After Johannes Stradanus. Courtesy of the Rijksmuseum-Stichting, Amsterdam. Library of Congress Cataloguing-in-Publication Data Historical painting techniques, materials, and studio practice : preprints of a symposium [held at] University of Leiden, the Netherlands, 26-29 June 1995/ edited by Arie Wallert, Erma Hermens, and Marja Peek. p. cm. Includes bibliographical references. ISBN 0-89236-322-3 (pbk.) 1. Painting-Techniques-Congresses. 2. Artists' materials- -Congresses. 3. Polychromy-Congresses. I. Wallert, Arie, 1950- II. Hermens, Erma, 1958- . III. Peek, Marja, 1961- ND1500.H57 1995 751' .09-dc20 95-9805 CIP Second printing 1996 iv Contents vii Foreword viii Preface 1 Leslie A.
    [Show full text]
  • Download 2014 Report in Pdf Format
    National Gypsum Company National Gypsum Company The custodian of two holy mosques king Salman Bin Abdul Aziz Al Saud His Royal Highness Prince His Royal Highness Mohammed bin Nayef bin AbdulAziz Al Saud Prince Muqrin bin Abdulaziz Al Saud Crown,Crown Prince Second Deputy Prime Crown Prince, Deputy Prime Minister Minister and Minister of Interior 1 Annual Report 2014 Annual Report 2014 National Gypsum Company 2 Annual Report 2014 National Gypsum Company National Gypsum Company AN EXTRACT FROM GOLDEN LOGBOOK OF NATIONAL GYPSUM COMPANY as we surpass the seventh - fifty year of contribution to building modern Saudi Arabia .it is due to bear in mind the early founders who established and developed the national gypsum company who founded strengthened the national edifice that the giant First put his daughters in the year 1378 Hijri. according to Royal Decree No. 552348/. the first plants of the National Gypsum Company were initially built in the city of Riyadh with a national capital of 12 million Saudi Riyals, rendering this company as third industrial enterprise ever established in Saudi Arabia . at the forefront of these early founders are HRH prince Abdul Rahman Ibn Abdul Aziz Al Saud, HRH Nawaf ibn Abdul Aziz Al Saud and Dr, Mohammad Khalid Khashoggi . Since it is early inception .NATIONAL Gypsum Company has been catering to the local building sector’s needs for gypsum. Over this period of time , the NGC has developed qualitatively in order to cope with the overall growth and progress of Saudi Arabia . in line with this constant growth , NGC built a additional plants in Dammam, Yanbu and expanded its existing plants in Riyadh, this expansion was to and extent that the production capacity of the company has exceeded the local market needs and extended to cover that the Gulf market and other neighboring countries .
    [Show full text]
  • Barite–Celestine Geochemistry and Environments of Formation Jeffrey S
    Barite–Celestine Geochemistry and Environments of Formation Jeffrey S. Hanor Department of Geology and Geophysics Louisiana State University Baton Rouge, Louisiana 70803 INTRODUCTION Minerals in the barite (BaSO4)–celestine (SrSO4) solid solution series, (Ba,Sr)SO4, occur in a remarkably diverse range of sedimentary, metamorphic, and igneous geological environments which span geological time from the Early Archean (~3.5 Ga) to the present. The purpose of this chapter is to review: (1) the controls on the chemical and isotopic composition of barite and celestine and (2) the geological environments in which these minerals form. Some health risks are associated with barite, and these are discussed near the end of this chapter. Although complete solid solution exists between BaSO4 and SrSO4 most representa- tives of the series are either distinctly Ba-rich or Sr-rich. Hence, it is convenient to use the term barite to refer to not only the stochiometric BaSO4 endmember but also to those (Ba,Sr)SO4 solid solutions dominated by Ba. Similarly, the term celestine will refer here not only to the stoichiometric SrSO4 endmember but to solid solutions dominated by Sr. Such usage is in accord with standard mineral nomenclature. The Committee on Mineral Names and Nomenclature of the International Mineralogical Association recognizes “celestine” as the official name for SrSO4. However, the name “celestite” is still commonly used in the literature. Geological significance of barite and celestine Most of the barite which exists in the Earth’s crust has formed through the mixing of fluids, one containing Ba leached from silicate minerals, and the other an oxidized shallow fluid, such as seawater, which contains sulfate.
    [Show full text]
  • Soil Processing Deliver Dirty Water (X M)
    National Aeronautics and Space Administration Mars Water Mining for Future Human Exploration Jan. 13,, 2016 Gerald (Jerry) Sanders NASA/JSC [email protected] Water on Mars (Simplified) Atmosphere Resource too scarce; not worth the effort . ppm levels Hydrated Soil Permafrost Icy Soils Recurring Slope Aquifers Lineae (RSL) . Water of hydration in . Subsurface . Shallow, nearly pure . Briny water has been . Suspected to be minerals ice/permafrost within ice in newly formed theorized as cause of >1 km below surface the top 5 meters in craters in mid-upper RSLs. <2 to ~13% by mass . Possible Special the mid latitudes latitudes. Fresh . Located at equator- Region . Primary at equator . Deeper ice/ impacts expose ice facing sunward-facing and lower latitudes permafrost may exist excavated from 0.3- sides of craters/ridges . At/near surface at lower latitudes 2.0 meters depth in the 30° to 50° . Concentration %? . Dirty ice at polar latitude range locations: Estimated . RSL sites and to be 90-100 wt% possibly the active H2O, mixed with dust gullies are Special from global dust Regions. storms . Not considered to be Special Regions unless heated to melting In Situ Water Extraction from Mars Soils Beamed Energy Down Hole Energy Electrical/thermal, microwave, or solar energy Microwave or solar energy Cold trap to Cold trap to collect water collect water vapor vapor Collection Collection device seals device seals Water vapor with surface Water vapor with surface released from released from heated soil Bore hole heated soil Bore hole before
    [Show full text]
  • GYPSUM EXTERNAL RENDERINGS of PARIS: HISTORY and FABRICATION Tiffanie Le Dantec
    GYPSUM EXTERNAL RENDERINGS OF PARIS: HISTORY AND FABRICATION Tiffanie Le Dantec To cite this version: Tiffanie Le Dantec. GYPSUM EXTERNAL RENDERINGS OF PARIS: HISTORY AND FABRICA- TION. Further Studies in the History of Construction: Proceedings of the Third Conference of the Construction History Society, 2016, 978-0-9928751-2-1. hal-01611366 HAL Id: hal-01611366 https://hal.archives-ouvertes.fr/hal-01611366 Submitted on 9 Oct 2017 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. EcUted by James W P Campbell NiebolasBm Mlebae1Drlver Mlebael Beaton Yltln8Pan Mlebael Tutton Christine Wall David Yeomans Published by The Construction History Society 1 Scroope Terrace Cambridge CB2 IPX www .construction.co.uk © 2016, First Edition ISBN 9 78-0-9928751-2- I Copyri ght © by the Constructi on H istory Society A li ri ghts reserved. These proceedings may not be rcproduced. ln who le or in part, in any fo rm w ithout permi ssion fro m th e Constructi on History Soc iety Formatting and layout by Yiting Pan First printed by Lulu print on demand fo r the Constructi
    [Show full text]
  • Gypsum As an Agricultural Amendment
    Bulletin 945 Authors Liming Chen Research Associate School of Environment and Natural Resources The Ohio State University Warren A. Dick Professor School of Environment and Natural Resources The Ohio State University Disclaimer This guide was funded in part by the U.S. Environmental Protection Agency (U.S. EPA) under a Resource Conservation Challenge grant. The contents of this guide do not necessarily reflect the views or policies of the U.S. EPA. The mention of trade names, individual companies, commercial products, or inclusion of web links to sites describing such materials or services is provided for information exchange and educational purposes only. Such mention does not constitute an endorsement, recommendation for use, or any form of implied warranty. Copyright © 2011, The Ohio State University Ohio State University Extension embraces human diversity and is committed to ensuring that all research and related educational programs are available to clientele on a nondiscriminatory basis without regard to race, color, religion, sex, age, national origin, sexual orientation, gender identity or expression, disability, or veteran status. This statement is in accordance with United States Civil Rights Laws and the USDA. Keith L. Smith, Ph.D., Associate Vice President for Agricultural Administration and Director, Ohio State University Extension TDD No. 800-589-8292 (Ohio only) or 614-292-1868 Contents Preface.........................................................................................4 Chapter 1: Sources and Properties of Gypsum.......................................................5
    [Show full text]
  • Replacement of Calcite by Gypsum R
    JOURNAL MINERALOGICAL SOCIET'' OF AXIERTCA 153 REPLACEMENT OF CALCITE BY GYPSUM R. E. R-r'rrcrn,Cornell Uni:tersity The writer was recently presented with some specimens of Tertiary fossil shells, which are interesting because they appear to represent a complete replacement of calcite by gypsum' The shells, whose structural features are well preserved, are mainly Vasum-like and, Ctabalithes-like forms. They were col- lected in Peru, South America, where they were found lying in the loose residual material derived from the weathering of a shale, and were distributed over a considerablearea. On superficial examination the specimensseemed to be normal calcareous shells; but closer study reveals occasional reflbcting surfaces of gypsum crystals on the surface of the shell as well as in the cavities of the same. An acid test shows only slight and much localized effervescence,leading one to the conclusionthat very little of the orisinal carbonate of lime remains. The shellshave retained practically their original shape and the surface irregularities are generally well preserved. Several of the specimens are unduly heavy due to the fact that the spiral cavities have been com- pletely filled with gypsum. Examination of thin sections of the shells under the microscope indicate quite clearly that gypsum has not only filled the shell cavities, but that the carbonateof lime of the shellitself has been almost completely replaced by that mineral. Some of the gypsum crystals in the cavities are quite large, several being noticet ftu! were six millimeters in diameter. The structure of the spiral shell is well outlined by a dark substance which appears to be limonite and around which the gypsum has formed.
    [Show full text]
  • Survey and Analysis of Plant Communities Growing on Gypsum
    Survey and Analysis Of Plant Communities Growing On Gypsum In The Western Australian Wheatbelt BOTANICAL CONSULTANTS REPORT FOR THE WHEATBELT NRM REGION AND THE DEPARTMENT OF ENVIRONMENT AND CONSERVATION WESTERN AUSTRALIA BY ANNE (COATES) RICK PO Box 36 NEWDEGATE WA 6355 Telephone (08) 98206048 Facsimile (08) 98206047 Email [email protected] 2011 TABLE OF CONTENTS Plant communities growing on Gypsum in the WA Wheatbelt SUMMARY--------------------------------------------------------------------------------- 4 ACKNOWLEDGMENTS---------------------------------------------------------------- 7 INTRODUCTION------------------------------------------------------------------------- 8 Background-------------------------------------------------------------------------- 8 Study Area--------------------------------------------------------------------------- 8 Gypsum in Western Australia----------------------------------------------------- 10 Properties of Gypsum Affecting Plant Growth--------------------------------- 13 Gypsophilous Plant Species ------------------------------------------------------ 13 Evolution of Gypsophiles--------------------------------------------------------- 15 Australian Research---------------------------------------------------------------- 15 Environmental impacts of gypsum mining-------------------------------------- 17 METHODS----------------------------------------------------------------------------------- 18 2009 Survey – Fieldwork---------------------------------------------------------- 18 Data Analysis------------------------------------------------------------------------
    [Show full text]