University of Pennsylvania ScholarlyCommons Theses (Historic Preservation) Graduate Program in Historic Preservation 1990 Granite Deterioration in the Graveyard of Saint James the Less, Philadelphia Kathryn Marit Sather University of Pennsylvania Follow this and additional works at: https://repository.upenn.edu/hp_theses Part of the Historic Preservation and Conservation Commons Sather, Kathryn Marit, "Granite Deterioration in the Graveyard of Saint James the Less, Philadelphia" (1990). Theses (Historic Preservation). 307. https://repository.upenn.edu/hp_theses/307 Copyright note: Penn School of Design permits distribution and display of this student work by University of Pennsylvania Libraries. Suggested Citation: Sather, Kathryn Marit (1990). Granite Deterioration in the Graveyard of Saint James the Less, Philadelphia. (Masters Thesis). University of Pennsylvania, Philadelphia, PA. This paper is posted at ScholarlyCommons. https://repository.upenn.edu/hp_theses/307 For more information, please contact [email protected]. Granite Deterioration in the Graveyard of Saint James the Less, Philadelphia Disciplines Historic Preservation and Conservation Comments Copyright note: Penn School of Design permits distribution and display of this student work by University of Pennsylvania Libraries. Suggested Citation: Sather, Kathryn Marit (1990). Granite Deterioration in the Graveyard of Saint James the Less, Philadelphia. (Masters Thesis). University of Pennsylvania, Philadelphia, PA. This thesis or dissertation is available at ScholarlyCommons: https://repository.upenn.edu/hp_theses/307 UNIVERSITVy PENNSYLVANIA. UBKARIES GRANITE DETERIORATION IN THE GRAVEYARD OF SAINT JAMES THE LESS, PHILADELPHIA Kathryn Marit Sather A THESIS in The Graduate Program in Historic Preservation Presented to the faculties of the University of Pennsylvania in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE 1990 Samuel Y. Harris, Lecturer, Historic Preservation Advisor V^eanne Marie Teutonico, Lecturer, Historic Preservation Reader ^©dvid G. De top^,top<5 l^rofess^or of/-^rchi tecture Graduate Group Chairman VC9 '^-^'3 ^7.^ /VA 10^ / / ^ PiWWSYLVANlA LIBRARIES To my Bister, Krista 11 CONTENTS ACKNOWLEDGMENTS iv CHAPTER 1 : INTRODUCTION CHAPTER 2 : GRANITE FORMATION, PROPERTIES, QUARRYING AND FINISHING TECHNIQUES CHAPTER 3 : MECHANISMS OF DETERIORATION 14 CHAPTER 4 : DATA COLLECTION CHAPTER 5 : ANALYSIS 49 CHAPTER 6 : OPTIONS FOR INTERVENTION CHAPTER 7 : CONCLUSION 70 APPENDIX A : ILLUSTRATIONS 72 APPENDIX B : GRANITE TOMBSTONE INVENTORY SHEETS 84 BIBLIOGRAPHY 115 111 ACKNOWLEDGMENTS I would like to thank my advisor, Samuel Y. Harris for his encouragement and knowledgeable advice; Jean Marie Teutonico for synthesizing technical and theoretical approaches; and all of the other people who shared their time and knowledge. I also would like to e>;pres5 my gratitude to the members of my family and my friends for their constant encouragement and support. iv CHAPTER 1: INTRODUCTION Although the quarrying of granite for use as a building and monumental stone dates back to ancient civilizations such as Egypt, the actual use was often reserved for sculpture and choice locations in temples and monuments, including the famous obelisks and veneer in a few small rooms in the Temple of Karnak . The extreme hardness of granite, as compared with other available stones like marble and limestone, precluded granite from widespread use as a building stone. With the mechanization of the quarry process, the advent of pneumatic hammers, and the development of carbide and diamond tipped saws, the hardness of granite became less of an economic consideration. The durability of granite, related to its low porosity and non-calcareous mineral structure, made granite a popular building material, both as a building stone and for monumental and sepulchral uses. Due to the relative durability and recent widespread usage in the United States, granite deterioration has received little attention outside of academic petro logical journals. There is a lack of information on tkie mechanisms of deterioration and options for intervention available to an architectural conservator when faced with a deteriorated granite object or building. After roughly one hundred years of exposure, it has become apparent that granite does in fact deteriorate, althoLigh at a slower rate than other corrrmon building stones. The superior qualities of granite as a building material led to its widespread use for tombstones, beginning in the last quarter of the nineteenth century. Marble and sandstone tombstones have been used in numerous studies as examples of stone weathering. The fact that the stones ^^re often placed in direct contact with the soil, sre relatively thin, and ^re exposed on all sides leads to accelerated weathering as compared with building stones which have some measure of protection provided by a roof and the surrounding stones. For these reasons, this study utilizes granite tombstones as examples of stone deterioration. The churchyard of St. James the Less, a National Landmark located in Philadelphia, contains many granite tombstones which exhibit differing types of deterioration. The examination of these tombstones and the determination of the causes and rates of deterioration should help determine the necessity for and possible methods of intervention. This case study will provide a review of the mechanisms of granite deterioration as they apply to gravestones, which when coupled with the analysis of the surface deterioration of the granite gravestones at Saint James the Less, may be applicable to other uses of granite as a building or monumental stone. ENDNOTES: CHAPTER 1 (1) Mary Winearls Porter, UJhat Rome Was Bull t With (London: Henry Frowde, 1907), 62. CHAPTER 2: GRANITE FORMATION, PROPERTIES, QUARRYING AND FINISHING TECHNIQUES The weathering characteristics of granite are in part determined by the formation process, the properties of the mineral constituents, and the methods used in the quarrying and dressing processes. An understanding of these properties and processes provides a basis for understanding the complex interactions between the granite and the environment which produce various types of surface deterioration on the tombstones. All igneous rocks are formed when magma, which is molten silica found below the earth's crust, makes its way into the earth's crust. If the magma is allowed to cool within the crust, the resultant rock is called intrusive or plutonic. These rocks are characterized by coarse grains, as the magma cools very slowly and large crystals are formed. If the magmra is extruded above the earth's surface the magma undergoes rapid cooling and the resultant grains are much finer. These rocks are called extrusive or volcanic. Granite is an intrusive rock that is exposed to the surface by the weathering of less durable rocks above it and by movements in the earth's surface. " . The coarse-grained or phaneritic texture of granite is important, as the larger the grain size, the more the minerals will behave according to their individual properties.-' The minerals formed in the crystallization of an igneous rock depend on the elements present in the original magma and upon the changing temperature of the magma as it cools. The minerals whxch make up granite are chiefly quartz and feldspar. Quartz comprises up to 25'/. of granite and is formed from silicon and oxygen." It is colorless when pure, but impurities can impart a light gray, yellow, pink or violet color. It has a glassy appearance and a hardness of 7 on the Mohs scale Plagioclase and orthoclase feldspar can constitute over 507. of granite. Both types of feldspar have a hardness of 6 and form elongated crystals in igneous rocks. Plagioclase feldspar forms from aluminum, silicon, oxygen, and either sodium or calcium, and varies in color from white to gray. Orthoclase feldspar contains potassium, aluminum, silicon, and oxygen, ranges in color from white to gray but is often a salmon pink color, and is much more common in granite than either the sodium- rich or calcium-rich plagioclase feldspars 8 other minerals present can include either mica in the form of muscovite or biotite, and amphibole, usually in the form of hornblende. The micas have a hardness of between 2-3 on the Mohs scale and can easily split into parallel sheets due to a weak bond between the more o strongly bonded layers. Muscovite ranges from a clear to a light gray, green or brown color, and is less common than biotite, which is characterized by a black, dark green or brown color. Although different in structure, both micas contain potassium, aluminum, silicon, oxygen, and hydrogen. Biotite also contains magnesium and iron as well. Amphibole is a comple;-; family of hydrous calcium, sodium, magnesium, iron, and aluminum silicates of which hornblende is a common member. The colors range from dark green to black and the mineral has a hardness of between 5 and 6 on the Mohs scale. •* Due to the mineral constituents and the process in which it is formed, granite e;;hibits properties which make it an ideal building and monumental stone. Granite has an extremely low porosity, between 0.3 and 1.5"/. .'••^ The bulk density (gm/cm3) is 2.5-2.8.-^-' Granite is also very hard due to the hardness of the minerals, and commonly has compressive and tensile strengths higher than other common building stones. Beyond the formation process and mineral properties of granite, the quarrying and cutting processes also affect the weathering