Download Sedimentary Rocks Lab Refer to Exercise #2 in you lab manual for

Name: ________________________________ Hour: ______
Sedimentary Rocks Lab
Refer to Exercise #2 in you lab manual for reference. (pgs 19-30)
Objectives:
1. Separate common sedimentary rocks into detrital or chemical based on their
properties.
2. Use a classification key to identify sedimentary rocks.
3. Identify the environments that form sedimentary rocks.
Introduction
To an Earth scientist, rocks represent much more than usable substances. They
are the material of the Earth; understanding heir origin and how they change allows us to
begin to understand earth and its processes. “The history of the Earth is written in the
rocks” (Tarbuck, Lutgens, Pinzke pg 19)
You will investigate some of the common sedimentary rocks that are found on
and near the earth’s surface by identifying them based on their properties. Sedimentary
rocks form from the accumulation of weathered rock particles called sediments. These
particles may be solid particles or material that was formerly dissolved and then
precipitated by either inorganic or organic processes. The process of lithification
transforms the sediment into hard rock. Since sedimentary rocks form at, or very near the
Earth’s surface, they often contain organic matter, or fossils, or both. The layering (or
bedding) that develops as sediment is sorted by, and settled out from a transporting
material (usually water or air) helps make sedimentary rocks recognizable.
Sedimentary Rocks Identification
Refer to Figures 2.10-2.17 of your lab manual for pictures of common
sedimentary rocks. Sedimentary rocks are made from either detrital or chemical
materials, and sometimes both.
Detrital material consists of mineral grains or rock fragments derived from the
process of mechanical weathering that are transported and deposited as solid particles
(sediments). Rocks formed in this manner are called detrital sedimentary rocks. The
mineral pieces that make up a detrital sedimentary rock are called grains (or fragments).
The identification of a detrital sedimentary rock is determined primarily by the size of the
grains or fragments. Mineral composition of the rock is a secondary concern.
Chemical material was previously dissolved in water and later precipitated by
either inorganic or organic processes. Rocks formed in this manner are called chemical
sedimentary rocks. If the material is the result of the life processes of water-dwelling
organisms- like a shell- it is said to be of biochemical origin. Mineral composition is the
primary consideration in the identification of chemical sedimentary rocks.
In this investigation, sedimentary rocks are divided into two groups, detrital and
chemical, based upon the type of material found in the rock.
Part 1: Examining Sedimentary Rocks
Examine the sedimentary rock specimens 1-4 in your tray. These rocks are made of
pieces or fragments and are called detrital sedimentary rocks. They do not include any
rocks that have abundant shells or shell fragments. Use these rocks to answer Q1 & 2.
1. Pick up each detrital sedimentary rock specimen and rub your finger over it to feel
the size of the grains or fragments. How many of your detrital specimens feel
rough like sand? How many feel smooth like mud or clay?
________ specimens feel rough
________ specimens feel smooth
2. Two minerals that often comprise the grains of detrital sedimentary rocks are
quartz and clay. Quartz is a hard (scratches glass) mineral with a glassy,
transparent to translucent luster. Clay is a soft (doesn’t scratch glass) mineral that
contains tiny particles. How many of your detrital sedimentary rock specimens
are made of quartz and how many appear to be made of clay?
________ have quartz
________ have clay
The remaining sedimentary rocks (specimens 5-9) are chemical sedimentary
rocks. They are composed of shells or shell fragments as well as crystals. Use these
specimens to answer Q 3.
3. As a result of their method of formation, many chemical sedimentary rocks are
fine to coarse crystalline, while others consist of shells or shell fragments. How
many of your chemical sedimentary rocks are crystalline, and how many contain
abundant shells or shell fragments?
________ specimens are crystalline
________ specimens contain shell or shell fragments
Part 2: Sedimentary Rocks and Environments
Sedimentary rocks are extremely important in the study of Earth’s history.
Particle size and the materials from which they are made often suggest something about
the place, or environment, in which the rock formed. The fossils that often are found in a
sedimentary rock also provide information about the rock’s history. Think of
sedimentary rocks as representing a “place” on Earth where sediment was deposited.
Figure 2.30 shows a few generalized environments (places) where sediment
accumulates. Often, an environment is characterized by the type of sediment and life
forms associated with it. Use Figure 2.30 to answer Q 4 & 5. Use pg 30 from your labe
manual for a colored image of Figure 2.30.
4. Imagine you are holding the sedimentary rock sandstone. Sandstones are formed
from sand. Where on Earth do you find sand, the primary material of sandstone,
being deposited today?
____________________________________________
5. Name the environment(s) where, in the past, the sediment for the following
sedimentary rocks may have been deposited.
Part 3: Sedimentary Rock Identification
Use the Sedimentary Rock Identification Key below to identify the sedimentary
rocks in your tray. Notice that the primary subdivisions for detrital rocks are based upon
grain size, whereas composition is used to subdivide the chemical rocks.
Sedimentary Rock Identification Key
Detrital
Chemical
Texture
Sediment Name
Rock Name
Composition
Texture
Rock Name
Coarse
Gravel (rounded)
Conglomerate
Calcite, fizzes in HCl
Fine
Limestone
Medium
Sand
Sandstone
Calcite, fizzes in HCl
Shell Fragment
Coquina
Medium
Sand
Banded Sandstone
Quartz
Fine, very light colored
Chert
Medium
Sand (with feldspar)
Arkose Sandstone
Gypsum
Fine light to pink
Rock Gypsum
Fine
Mud
Shale
Plant Fragments
Fine very light weight
Bituminous Coal
Using the Identification Key above, fill in the identification chart below.
Rock # Detrital/Chemical
1
2
3
4
5
6
7
8
9
10
Texture
(grain size)
Sediment Name (Detrital) or
Composition (Chemical)
Environment formed?
(use Fig 2.30)
Rock Name