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1 1 1 1 1 1 1 1 GENERAL NOTES Sedimentary Rock Classification DESCRIPTIVE ROCK CLASSIFICATION: Sedimentary rocks are composed of cemented clay, silt and sand sized particles. The most common minerals are clay, quartz and calcite. Rock composed primarily of calcite is called limestone; rock of sand size grains is called sandstone, and rock of clay and silt size grains is called mudstone or claystone, siltstone, or shale. Modifiers such as shaly, sandy, dolomitic, calcareous, carbonaceous, etc. are used to describe various constituents. Examples: sandy shale; calcareous sandstone. LIMESTONE Light to dark colored, crystalline to fine•grained texture, composed of CaCo,, reacts readily with HCI. DOLOMITE Light to dark colored, crystalline to fine-grained texture, composed of CaMg(CO~):, harder than limestone, reacts with HCI when powdered. CHERT Light to dark colored, very fine-grained texture, composed of micro-crystalline quartz (SiO,), brittle, breaks into angular fragments, will scratch glass. SHALE Very fine-grained texture, composed of consolidated silt or clay, bedded in Ihin layers. The unlaminated equivalent is frequently. referred to as siltstone, claystone or mudstone. SANDSTONE Usually light colored, coarse to fine texture, composed o(cemented sand size grains of quartz, feldspar, etc. Cement usually is silica but may be such minerals as calcite, ironoxide, or some other carbonate. CONGLOMERATE Rounded rack fragments of variable mineralogy varying in size from near sand to bouidersize but usually pebble to cobble size ('h inch to 6 inches). Cemented together with various cemen- ting agents. Breccla is similar but composed of angular, fractured rock particles cemented together. PHYSICAL PROPERTIES: DEGREE OF WEATHERING Slight Slight decomposition of parent material on joints. May be color change. Moderate Some decomposition and color change throughout. High Rock highlydecomposed, may be ex• tremely broken. BEDDING AND JOINT CHARACTERISTICS Bed Thickness Joint Spaeing Dlmenclone Very Thick Very Wide >10' Thick Wide 3' • 10' Medium Moderately Close 1' • 3' Thin Close 2^ - 1' Very Thin Very Close .4" • 2' Laminated - .1°- .4' Bedding Plane HARDNESS AND DEGREE OF CEMENTATION Limestone and Dolomite Joint A plane dividing sedimentary rocks of the same or different Ilthology. Fracture In rock, generally more or less vertical or transverse to bedding, along which no appreciable move- ment has occurred. Generally applies to bedding plane with an unspecified degree of weathering. Hard Difficult to scratch with knife. Moderately Can be scratched easily with knife, Seam Hard cannot be scratched with fingernail. Soft Can be scratched with fingernail. Shale, siltstone and claystone Hard Can be scratched easily with knife, cannot be scratched with fingernail. Moderately Hard Can be scratched with fingernail. Soft Can be easily dented but not molded with fingers. Sandstone and Conglomerate Well Capable of scratching a knife blade. Cemented Cemented Can be scratched with knife. Poorly Can be broken apart easily with Cemented fingers. 1 t~rracon SOLUTION AND VOID CONDITIONS Solid Contains no voids. Vuggy (Pitted) Rock having small solution pits or cavities up to 'h inch diameter, fre- quently with a mineral lining. Porous Containing numerous voids, pores, or other openings, which may or may not interconnect. Cavernous Containing cavities orcavems, some- times quite large.