CONTENTS
Abstract    1
Introduction    2
        Purpose and scope    3
        Previous heavy-mineral studies    3
        Study methods    5
               Borehole sampling.    5
               Laboratory analyses    5
Geologic framework of Long Island     6
Heavy minerals and sedimentary organic matter    8
        Vertical variations    8
        Lateral variations.    8
        Grain size   12
Pyrite and marcasite in the Magothy aquifer.   12
        Mineralogic and lithologic description of selected.13
               Landscape Drive cores   13
               Adams Avenue cores.   13
               Locust Drive cores.   14
               Margin Drive cores.   14
               Moriches-Riverhead Road cores and Scuttlehole Road cores   16
        Mineral reactivity   16
Summary and conclusions   20
References cited   20

FIGURES
1. Map of Long Island, N.Y., showing locations of the borehole sites and line of section A-A' along Nassau-Suffolk County border, Long Island, N.Y.    3
2. Hydrologic section A-A' along the Nassau-Suffolk County border, showing projections of nearby boreholes studied in this report     4
3. Photographs of lignite from the Magothy aquifer, Long Island:
 A. laminae or thin beds in split-spoon core sample.
 B. Lignite "wood" pieces from site LO.
 C. Secondary electron image of lignite wood cells from site AD.   10
4. Plots showing abundance of (A) silt and clay, and (B) total sulfur and organic carbon, in core-sample sediments relative to altitude below sea level, and log percent  (C) total sulfur and D) silt and clay, as a function of log organic carbon percentage of core samples from borehole S79407T, Suffolk County.11
5. Photographs of pyrite and marcasite from the Magothy aquifer in Suffolk County:
 A. pyrite crystals within lignite from site LO.
 B. pyrite crystals in a spheroid aggregate from site SC.    
 C. Interstitial marcasite in quartz sand from site AD   13
6. Scanning-electron microscope images showing etched octahedral pyrite crystals from site LA, Suffolk County:
 A. Random etchings.
 B. Localized etching.   14                                                                                                 
7. Scanning-electron microscope images of iron-sulfide minerals from site AD, Suffolk County:
 A. Etched octahedral pyrite crystals,
 B. Interstitial marcasite cement.
 C  Platey marcasite crystals in marcasite cement.
 D. Parallel growth steps, of platey marcasite.         
 E. Cockscomb marcasite   15        
8. Scanning-electron microscope images of samples from site LO, Suffolk County: A. Pyrite crystals and lignite wood-cell structures. B. Octahedral pyrite crystals  16        
9. Scanning-electron microscope images of samples from site MA near the southern shore of Suffolk County:
 A. Cockscomb-growth marcasite crystals overgrown with smaller crystals of octahedral pyrite.
 B. Cubo-octahedral pyrite crystals.
 C. Framboidal pyrite.
 D. Octahedral pyrite on lignite.
 E. Cubo-octahedral pyrite.
 F. Glauconite  17      
10. Scanning-electron microscope image showing poorly crystalline marcasite cement with stalactite-shaped crystals from site MO, Suffolk County.  18      
11. Cubic pyrite from site SC, Suffolk County:
 A. "Ball," about 1 centimeter in diameter.          
 B. Interlocking cubic {100} crystals on surface of ball;
 C. Thin section of "ball" showin wedge-shaped crystals radiating the center.
    Arrows near center indicate lenticular lignite pieces.
 D. Magnified image showing the internal radial texture   18      
12. Wavelength-dispersive maps showing the distribution of selected elements (as indicated by light color) associated with iron-bearing minerals and rutile among quartz grains, surrounded by pyrite cement in sample from site MA, Suffolk County, at 117 m below sea level  19      
TABLES        
1. Altitudes, hydrogeologic units, and methods of analysis for borehole samples from Nassau and Suffolk Counties, Long Island.   7        
2. Most abundant heavy minerals in sand-size fractions in borehole cores from Nassau and Suffolk Counties, Long Island.   9