GEORGIA STATE DIVISION OF CONSERVATION DEPARTMENT OF MINES, MINING AND GEOLOGY GARLAND PEYTON, Director THE GEOLOGICAL SURVEY Bulletin No. 61 GEOLOGY OF THE STONE MOUNTAIN-LITHONIA DISTRICT, GEORGIA By Leo Anthony Herrmann ATLANTA 1 9 5 4 LETTER OF TRANSMITTAL Department of Mines, Mining and Geology Atlanta, April 15, 1954 To His Excellency, Herman E. Talmadge, Governor Commissioner Ex-Officio of State Division of Conservation Sir: I have the honor to submit herewith Georgia Geological Survey Bulletin No. 61, "Geology of the Stone Mountain­ Lithonia District, Georgia". This report was prepared by Dr. Leo A. Herrmann as a Doctor's thesis in geology at The Johns Hopkins University. It represents a thorough and original investigation of one of Georgia's most important granite districts. Thus, its publica­ tion will be welcomed by our granite producers and by all who are interested in the science of granite. Very respectfully yours, GARLAND PEYTON Director III 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 •1 1 1 1 1 1 1 1 1 1 1 1 1 1 CONTENTS Page ABSTRACT ···----------------·-----------· ······----······-----··------XV INTRODUCTION ------------------·---------- ----------------------····· 1 Purpose of the ReporL __________ . __________________ _ 1 Location of the District .. _________ ·------------------------- __ _ 1 Physiography --------------------------------------------------------------- 2 Weathering --------------------------------------- ·--------------------- __________ _ 3 Previous Work -------------------------------------------------------------·------ 6 Present Study -----------------------··--------·----------------------···----------­ 6 Acknowledgments -------------------------------------------------------------- 7 PETROGRAPHY _________________________ _ 8 Migmatite ---------------------------------·- .. ·----------------- _ 8 Lithonia gneiss ____________________ _ 8 Metamorphic Rocks ________________________ --------------------- . _ 15 General statement _____________ _ 15 Distribution ---------------------------------------------------------· 17 Garnet-mica schist and muscovite quartzite __ .___ 17 Biotite gneiss ----------------------·-· ---------------------··------·- ... 19 Muscovite-quartz schist _____ .. .. -------------· ____ ___ __ 20 Amphibolite ---------------·-----------·-- _________________ ...... _____ 20 Biotite-hornblende gneiss ...... _ ----------· 26 Porphyroblastic biotite gneiss _ ....... __ 27 Minor rock types ________________ .. ... .. __________ 28 Igneous Rocks _ ... ·--------·-- __ -·--- __ ...... ________ 29 Stone Mountain granite (quartz-monzonite) _ 29 Pegmatite dikes _____________________ ·------------- 32 Aplite dikes __________________________________ ---·------------ ... .... 33 Diabase dikes ---------------------------------------------------- ·- 33 Alluvium __________________________________ ... __ .. ..... ______ . ____ . ___ .... 33 STRUCTURAL GEOLOGY ---------------------------------- .. .. 34 Structures of the Lithonia Gneiss. ___ ·-·----------- 34 Banding _____________________________________________ . _____________ ..... _____ . __ _ 34 Garnetiferous layers ·-----------·---------------------------- __________ 34 Flow fo 1ds ________________________________________________________________ . __ __ _ 34 Ptygmatic folds ---------------------------------------------------·-- ____ . 35 Shear zones --------------------------------------------------------- ___________ 36 Mica lineation ______ ... ·----- ____ ____ ____ __ ______ ____________ __ __ __ __ __ __ __ __ _ 3 8 Joints __ .. _______________________ . _____________ .. ______________________ .. ___ ______ __ 3 9 Structures of selected exposures of the Lithonia gneiss 41 v CONTENTS Page Structures of the Metamorphic Rocks ________________________________ 43 Schistosity ---------------------------------------------------------------------- 43 Foliation -------------------------------------------------------------------------- 43 Banding -------------------------------------------------------------------------- 43 Compositional layering -------------------------------------------------- 48 Minor folds ---------------------------------------------------------------------- 48 Longitudinal folds ____________________________________________________ :_____ 50 Undulatory folds ------------------------------------------------------------ 52 Transverse folds ------------------------------------------------------------ 52 Crenulations -------------------------------------------------------------------- 52 Lineations ------------------------------------------------------------------------ 52 Faults ------------------------------------------------------------------------------ 54 Joints ------------------------------------------------------------------------------ 55 Structures of the Stone Mountain Granite (quartz-monzonite) --------------------------------------- ____ ________ ___ 55 Flow structures -------------------------------------------------------------- 55 Xenoliths ------------------------------------------------------------------------ 57 Tourmaline clusters -------------------------------------------------------- 60 Joints ________ ------------------ ___ ___ __ ______________________ __ _______ __ __ ______ __ _ 6 0 Relationship of Structures to Deformation ________________________ 62 General statement ------------------------------------------------------- ___ 62 Coordinates of deformation____________________________________________ 62 Major axis of uplift ________________________________________________________ 62 Minor axes of uplift ________________________________________________________ 62 Mica lineation ------------------------------------------------------------- ___ 63 Shear zones -------------------------------------------------------------------- 63 Joints ___________________ ___ ____ ________ _________ ____ _________ __ ___ ______ __ ____ __ _ _ _ 63 Relationship of Igneous Intrusions to Deformation__________ 64 Petrofabric Analysis ---------------------------------------------------------- 64 Method ---------------------------------------------------------------------------- 6·1 Fabric diagrams ------------------------------------------------------------ 65 Discussion ---------------------------------------------------------------------- 65 PETROGENESIS -------------------------------------------------------------------- 68 Origin of the Lithonia Gneiss ____________________________________________ 68 General statement ---------------------------------------------------------- 68 Banding and garnetiferous layers _________ : ________________________ 68 Potash metasomatism ---------------------------------------------------- 70 Migmatization ---------------------------------------------------------------- 71 Origin of the Amphibolites____________________________________________________ 73 VI CONTENTS Page General statement ---------------------------------------------------------- 73 Igneous origin ---------------------------------------------------------------- 7 4 Sedimentary origin -------------------------------------------------------- 7-J Origin of the Biotite-Hornblende Gneiss __________________________ 75 Origin of the Stone Mountain Granite ______________________________ 75 METAMORPHISM ---------------------------------------------------------------- 76 General Statement -------------------------------------------------------------- 76 Staurolite-Kyanite Subfacies -------------------------------------------- 76 Sillimanite-almandine Subfacies -------------------------------------- 76 Mineralogical Changes During Progressive Metamorphism ---------------------------------------------------------------- 76 Causes of Metamorphism ____________________________________________________ 77 GEOLOGICAL HISTORY AND CONCLUSIONS________________ 78 THE STONE INDUSTRY ________________________________________________________ 80 History -------------------------------------------------------------------------------- 80 Types of Stone ____________________________________________________________________ 83 Stone Mountain granite (quartz-monzonite)________________ 83 Lithonia gneiss ---------------------------------------------------------------- 84 Panola granite ---------------------------------------------------------------- 85 Physical Characteristics of Granite and Gneiss________________ 85 General statement ---------------------------------------------------------- 85 Hardness ........ ---------------------------------------------------------------- 86 Crushing strength ---------------------------------------------------------- 86 Structure ------------------------------------------------------------------------ 86 Texture ---------------------------------------------------------------------------- 87 Mineral composition ------------------------------------------------------ 87 Color -------------------------------------------------------------------------------- 87 Quarrying Methods ------------------------------------------------------------ 88 Building stone --'------------------------------------------------------------- 88 Crushed stone ---------------------------------------------------------------- 89 Uses of Stone ________________________________________________________________________ 89 DESCRIPTION OF QUARRIES ____________________________________________ 90 General Statement -------------------------------------------------------------- 90 Stone Mountain Granite (quartz-monzonite)