Laboratory Manual for Introductory Geology 4e

EXERCISE 6.1
Looking at Weathering Products (continued )
Name:
Course:
(iii) AlI fine-grained clay minerals with some hematite and limonite
(iv) A mixture of quartz grains and clay minerals
(v) Rock fragments composed of Ca-plagioclase and pyroxene
Section:
Date:
(c) Rank the following environments in the order in which you would expect sediments to become mineralogically
mature, from slowest to fastest. (Hint: Think about the temperature and the amount of rainfall available.)
desert tropical rain forest temperate climate
Explain your reasoning.
(d) Which of the following mineral assemblages (from question b) are mineralogically mature? Which are
mineralogically immature?
(i) All quartz grains
(ii) Nearly equal amounts of quartz, K-feldspar, and Na-plagioclase with a small amount of hematite
(iii) All fine-grained clay minerals with some hematite and limonite
(iv) A mixture of quartz grains and clay minerals
(v) Rock fragments composed of Ca-plagioclase and pyroxene
6.3 The Basic Classes of Sedimentary Rocks
Geologists recognize many kinds of sedimentary rocks, each with a name based
on the nature of the material that the rock contains and the process by which it
formed. They use a simple classification scheme that groups all sedimentary rocks
into four major classes—clastic, chemical, biochemical, and organic—based on the
origin of the particles of which they are made. In this section, we will first examine
these classes and then introduce a more comprehensive classification scheme that
includes chemical and mineral composition.
6.3.1 Clastic Sedimentary Rocks
Clastic sedimentary rocks form from clasts (mineral grains or rock fragments) produced
by physical weathering of previously existing rocks. Clastic rocks have a characteristic
texture in which discrete grains are held together by a chemical cement or by
a very fine-grained clastic matrix. Of the most common clastic sedimentary rocks, the
6.3 THE BASIC CLASSES OF SEDIMENTARY ROCKS
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