From the inside and out, Earth contains solid matter of all shapes, sizes, and colors. Our planet comprises thousands of different solids that have changed in abundance and composition throughout its long 4.54 billion year history. These solids are called minerals and rocks and they have literally built the Earth. Every solid foundation, every grain of sand, or gigantic mountain is built of individual rocks and minerals.
Rocks and minerals are not the same, but they are related. A rock is defined as a substance that contains at least one mineral or mineraloid. Thus, rocks are made out of minerals. In geology, a mineral is an inorganic, crystalline solid with a predictable chemical composition. Examples of rock names are: granite, basalt, limestone, sandstone. Examples of mineral names are quartz, mica, pyrite, olivine, etc.
Minerals make up rocks, with some exceptions. A rock can be a mineral. That happens when the rock is completely made out of a single mineral, for example, salt rock, which is composed of the mineral halite (NaCl). Another example is gypsum rock. The mineral gypsum (CaSO4) is very abundant and can form entire layers or rocks. Some rocks contain solidified organic matter (coal) or amorphous glass (obsidian). These solids do not fit the definition of mineral. They are examples of mineraloids (like-minerals). All rocks on Earth’s surface can be divided into three categories based on how they form: Igneous, Sedimentary, and Metamorphic. Igneous rocks crystallize from molten material, Sedimentary rocks cement from weathered sediment or precipitate from chemical ions, and Metamorphic rocks are warped products of preexisting rocks under heat and pressure.
Identifying rocks and minerals gives geoscientists a lot of key advantages, such as
- Predicting which regions or formations could be susceptible to hazards such as sinkholes or landslides.
- Finding economic resources such as precious metals, fossil fuels, and building materials.
- Determining locations of freshwater resources.
- Identifying hazardous materials.
Mastering the art of rock and mineral identification can save lives and build livelihoods. This chapter has a lot of tricks and techniques to get us started!
At the end of this chapter, you will be able to…
- Describe the characteristics of minerals and their identifying physical properties.
- Identify major rock-forming minerals and their impact on society.
- Explain the rock cycle and the processes that form different rocks.
- Characterize the identifying properties of igneous, sedimentary, and metamorphic rocks.
- Identify important rocks in the igneous, sedimentary, and metamorphic groups and their use in society.
a solid, inorganic, and crystalline substance that has a predictable chemical composition and form by natural processes.
a substance that contains at least one mineral or mineraloid.
An organic sedimentary rock formed by the compaction of plant and animal organic matter over millions of years.
A felsic, extremely smooth, fine-grained igneous rock that is glassy in texture. Obsidian is primarily composed of amorphous silica and displays conchoidal fracture.
solid substances, typically in rocks, that fall short of the definition of "mineral".
Rocks that crystallize from molten materials beneath the Earth surface or from volcanic processes.
rocks that cement together from weathering products, either from sediments or chemical ions in water.
Rocks that form when any type of preexisting rock is warped or transformed under elevated temperatures and pressures.
an extreme natural event that is a threat to life and property