Laboratory #3: Sedimentary Rocks

Laboratory #3: Sedimentary Rocks

Materials Needed (to be provided by the instructor):

1.  Sedimentary Rocks Set

2.  Scratch Glass, Porcelain Plate, Copper Penny, Iron Nail, Magnets, HCl

3.  Hand lens

Introduction to Sedimentary Rocks

Sedimentary rocks form in two stages. First, a sediment is formed; second, the sediment is lithified (literally, turned to stone) to become a rock.

Sediment / Rock Name
Gravels / Conglomerate
Breccia
Sand / Quartz sandstone
Arkose
Silts / Siltstone
Clays or muds / Mudstone
Claystone
SiO2 precipitate / Chert
NaCl precipitate / Halite (rock salt)
Lime mud
Lime mud with fossils / Limestone
Fossiliferous limestone
Coquina
Plant remains / Coal
Sediments to Sedimentary Rocks
Sediment Name / Grain Size / Rock Name
Gravel / 2 mm or larger / Conglomerate
Sand / 1/16 – 2 mm / Sandstone
Silt / 1/256 – 1/16 mm / Siltstone
Clay / Less than 1/256 / Claystone
A combination of silt and clay creates a mudstone

There are three types of sediment:

Clastic or detrital sediment – formed from the mechanical weathering and erosion of other rocks into broken bits of rock and mineral pieces. These broken rock and mineral fragments – also called grains - form sediments, which are transported from their original source and deposited elsewhere. You can distinguish clastic sediments as they consist of loose grains separated from one another by spaces. Loose sediments – clays, silts, sands, gravels, boulders, etc. – are held together with either a natural cement or matrix.

Chemical sediment – forms via the chemical precipitation of compounds out of water (usually seawater). In most chemical sediments, the compounds precipitated out of the water crystallize to form interlocking boundaries with hardly any spaces between the crystals.

Biochemical or bioclastic sediment – form from the accumulation of parts of organisms.

These three types of sediments may remain separate from one another, or may mix together.

The Lab

The object of the lab is to be able to identify the various types of sedimentary rocks based upon their composition and texture. First, identify the type of sediment the rock is composed of. Is the rock comprised of sand, pebbles, or shells? From here, you should be able to determine if the rock is clastic, chemical or bioclastic/biochemical. Next, examine each rock and find a feature or physical property that is unique (or relatively unique) to that rock type. Does it effervesce with HCl? Any fossils? Use the attached charts to help you in identifying the rocks.

Identification of Sedimentary Rocks

DETRITAL / Particle size / Physical properties / Rock name
Coarse (>2 mm)
pebbles and cobbles / Abraded (rounded) pebbles in sandstone, looks like concrete / CONGLOMERATE
Angular fragments show no signs of abrasion / BRECCIA
Medium (1/16th mm)
like coarse sandpaper / SANDSTONES / Dark sand-sized rock fragments impart a salt and pepper appearance; usually rich in clay / GRAYWACKE SANDSTONE
Abundant grains of feldspar are typically weathered to dull white or dull pink; commonly with some amount of clay / ARKOSE SANDSTONE
Relatively pure content of quartz grains; some examples are very porous. / QUARTZ SANDSTONE
Fine (1/256 - 1/16 mm)
like a fine nail file / MUDSTONES / Feels gritty, grains barely detectable with the unaided eye / SILTSTONE
Very fine (<1/256 mm)
grains not visible / Smooth to very slightly gritty; grains are not detectable with the unaided eye, slick when wet. / CLAYSTONE
Smooth to slightly gritty, grains not detectable with the unaided eye, fissile (i.e., breaks into sheets), slick when wet. / SHALE
BIOCHEMICAL / BIOCLASTIC / Constituents / Physical properties / Rock name
Calcite shell fragments / LIMESTONES / Shells packed together and cemented with transparent calcite, or "floating" in opaque lime mud / FOSSILIFEROUS LIMESTONE
Shells packed together and slightly cemented with calcite, very porous / COQUINA
Shells too small to be seen with the unaided eye, chalky or powdery, typically white to light gray to light brown / CHALK
Plants / Brown, fibrous, soft, porous; plant fragments visible / PEAT
Brown to black, non-porous, sooty, commonly spotted with yellowish sulfur compounds. / BITUMINOUS COAL
Silicious animals and plants / Extremely fine crystalline quartz (hardness = 7); crystals too small to be seen, conchoidal fracture, very sharp edges. / CHERT (FLINT)
CHEMICAL / Minerals / Physical properties / Rock name
Halite / EVAPORITES / Cubic crystals and cubic cleavage usually apparent, hardness = 2.5, salty taste / ROCK SALT
Gypsum / Soft (hardness = 2), very fine crystals impart sugary appearance, usually white or pink / ROCK GYPSUM
Calcite / LIMESTONES / Coarsely crystalline, typically yellow, red and brown bands / TRAVERTINE
Fine-grained character resembles that of mudstone, slightly conchoidal fracture, and slightly sharp edges. / MICRITE
Sand-sized grains of calcite called ooids; white to gray; a broken ooid exhibits concentric banding about the nucleus / OOLITE
Dolomite / Texture ranges from that of mudstone to that of travertine, many samples appear sugary / DOLOSTONE
Quartz / Extremely finely crystalline quartz (hardness = 7), crystals too small to be seen, conchoidal fracture, very sharp edges. / CHERT

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Sedimentary Rock Identification Table Name ______/ NAME / Chert / Breccia / Rock salt (Halite) / Anthracite coal / Limestone / Arkose sandstone / Fossiliferous limestone / Coquina / Limey siltstone / Shale / Conglomerate / Sandstone
ORIGINAL SEDIMENT / Silica mud / Angular gravels / Evaporated sea water / Peat bogs / Lime mud / Decomposed granite / Lime mud with critters / Lime mud and shells / Mix of lime mud and silt / Silt / Rounded gravel / Sand
OTHER
(Bedding, fossils, etc.) / Very hard! / Angular gravel / Tastes salty / Fizzes with HCl / Feldspars in matrix / Fossils! Fizzes with HCl / Lots of shells, fizzes with HCl / Lightly fizzes with HCl / May have bedding / Rounded gravel / Red in color, may have bedding
GRAIN SIZE (clay, sand, gravel) / Fine (clay/mud) / Coarse (gravel) / Coarse / Fine / Fine (mud) / Sand / Coarse / Coarse / Fine (mud) / Fine (mud) / Coarse (gravel) / Medium (sand)
DETRITAL/ CHEMICAL / BIO / Chemical / Detrital / Chemical / Biochemical / Chemical / Detrital / Biochemical / Biochemical / Chemical & detrital / Detrital / Detrital / Detrital
Sample # / 1 / 2 / 3 / 4 / 5 / 6 / 7 / 8 / 9 / 10 / 11 / 12

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