Download Sedimentary Rock Identification Chart

Sedimentary Rock Identification
Sedimentary Rocks
Sedimentary rocks are rocks composed of sediment. Sediment is deposited in a number of environments of
deposition, by both moving air and moving water. Sedimentary rock identification is primarily based on composition.
Texture will still be used but in a different sense than for igneous rocks.
Texture
Texture of sedimentary rocks in this lab will be taken to indicate origin or type of sediment found in the rock. Three
types of "texture" will be used - clastic, chemical, and biologic.
Clastic Rocks
Clastic sedimentary rocks contain clasts. These are fragments or pieces of rock or minerals. The composition of clastic
sedimentary rocks is divided into three types - clay/silt, sand and gravel. Clay and silt are less than 1/16 mm. These
are not visible to the unaided eye. Sand is clasts between 1/16 and 2 mm in size, and gravel is greater than 2 mm.
Chemical Rocks
Chemical sedimentary rocks are identified by identifying the mineral from which they are composed. In this lab there
are four minerals that need to be identified - quartz, halite, gypsum and calcite. Quartz has a hardness of 7 and is very
difficult to scratch, even with a good quality knife blade. Gypsum is relatively soft (Hardness =2) and can be scratched
easily with a fingernail. Halite is common table salt and is most easily identified by taste. However, this is not a
sensible practice in a large lab with many different people handling the samples. Halite has a hardness of 2.5 and
cannot be scratched by a fingernail (unpolished fingernail). Calcite readily reacts with a small drop of HCl.
Biologic Rocks
Biologic sedimentary rocks are which form as the result of the accumulation of organic material or biologic activity.
Coal is usually obvious to most students even though few people seem to have ever actually examined it up close.
The dark brown to black color is the most obvious charateristic. Coquina and limestone are both composed of calcite .
Coquina is composed almost entirely of shell or fossil fragments. Limestone may or may not contain fossils fragments.
Both will react to HCl. Limestone containing fossils is referred to as fossiliferous limestone.
Sedimentary Rock Identification Chart
TEXTURE
Clastic
Chemical
Biologic
GRAIN SIZE
COMPOSITION
ROCK NAME
>2 mm
rounded quartz, feldspar and rock fragments
Conglomerate
>2 mm
angular quartz, feldspar and rock fragments
Breccia
1/16 - 2 mm
quartz, feldspar
Sandstone
>1/16 mm
feldspar, quartz
Arkose
<1/16 mm
quartz, clay minerals
Siltstone
(Mudstone, Shale)
<1/256 mm
quartz, clay minerals
Claystone
silica (quartz)
Chert
dolomite
Dolostone
calcite
Limestone
halite
Rock Salt
gypsum
Rock Gypsum
silica (quartz)
Chert
loosely compacted organic material and plant fragments
Peat
densely compacted organic material and plant fragments
Bituminous Coal
calcite
Limestone
calcite, micro-skeletal fragments
Chalk
calcite, almost entirely shell and skeletal fragments
Coquina
calcite with some shell and skeletal fragments
Fossiliferous Limestone
dolomite with some shell and skeletal fragments
Fossiliferous Dolostone
Select a Sample to Identify:
1 •2 •3 •4 •5 •6 •7 •8 •9 •10 •11 •12
Metamorphic Rock Identification
Metamorphic Rocks
Metamorphic rocks are rocks that have undergone a change from their original form due to changes in
temperature, pressure or chemical alteration. The classification of metamorphic rocks is based on the minerals
that are present and the temperature and pressure at which these minerals form. Determination of this information
is not easily accomplished in this lab. Therefore, a simplified system is used based on texture and composition.
Texture
Texture is divided into two groups. Foliated textures show a distinct planar character. This means that the
minerals in the rock are all aligned with each other. This planar character can be flat like a piece of slate or folded.
Non-foliated textures have minerals that are not aligned. Essentially, the minerals are randomly oriented.
Foliation
Foliated textures show four types of foliation. Slaty cleavage is composed of platy minerals that are too small to
see. Typically, these rocks split along parallel, planar surfaces. Phyllitic foliation is composed of platy minerals
that are slightly larger than those found in slaty cleavage, but generally are still too small to see with the unaided
eye. The larger size gives the foliation a slighly shiny appearance. Schistose foliation is composed of larger
minerals which are visible to the unaided eye. Platy minerals tend to dominate. Gneissic banding is the easiest of
the foliations to recognize. It is composed of alternating bands of dark and light minerals.
Non-Foliation
Non-foliated textures are identified by their lack of planar character. Further identification of non-foliated rocks is
dependent on the composition of the minerals or components in the rock. Anthracite coal is similar to bituminous
coal. Both are black in color , and is composed of carbon. Anthracite coal is generally shiny in appearance and
breaks with a conchoidal fracture (broken glass also shows this type of fracture). Metaconglomerate is composed
of pebbles and gravel that have been flattened due to directed pressure. Quartzite is composed of quartz sand
grains. Quartz has a hardness of 7, which makes it difficult to scratch. Marble is composed of calcite and will
readily react to a small drop of HCl.
Metamorphic Rock Identification Chart
TEXTURE
Foliated
FOLIATION
COMPOSITION
TYPE
PARENT
ROCK
ROCK NAME
slaty
mica
Regional
Mudstone
Slate
phyllitic
quartz, mica, chlorite
Regional
Mudstone
Phyllite
schistose
mica, quartz
Regional
Slate
Schist
schistose
amphibole,
plagioclase
Regional
Basalt or
Gabbro
Amphibolite
Regional
Schist
Gneiss
Contact or
Regional
Bituminous
Coal
Anthracite Coal
gneissic banding feldspar, mica, quartz
carbon
Non-Foliated
quartz, rock
fragments
Contact or
Conglomerate Metaconglomerate
Regional
calcite
Contact or
Regional
Limestone
Marble
quartz
Contact or
Regional
Sandstone
Quartzite
Select a Sample to Identify:
1 •2 •3 •4 •5 •6 •7 •8 •
Link for Sedimentary Rock ID
http://facweb.bhc.edu/academics/science/harwoodr/geol101/Labs/Sediment/index.htm
Link for Metamorphic Rock ID
http://facweb.bhc.edu/academics/science/harwoodr/Geol101/Labs/metamorf/