Minerals and Rocks
From the inside and out, Earth contains solid matter of all shapes, sizes, and colors. Our planet contains thousands of different types of solids that have changed in abundance throughout its long 4.54 billion year history. These are 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.
Although they are both solids that compose the Earth, rocks and minerals are NOT the same thing! A rock is defined as a substance that contains at least one mineral or mineraloid. We will get into the exact definition in the next part, but suffice it to say, a mineral is an inorganic, crystalline solid with a predictable chemical composition.
The key difference between rocks and minerals is that a rock can contain more than one mineral and does not often have a predictable chemical composition as a result. Additionally, some rocks don’t have minerals within them at all; they can contain solidified organic matter (coal) or amorphous glass (obsidian). These solids are examples of mineraloids.
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.
Being able to identify rocks and minerals give 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, minerals, and ores
- Determining locations in which oil and gas deposits reside underground
- Understanding groundwater resources
Mastering the art of rock and mineral identification can save lives and build livelihoods. Luckily for us, this chapter has a lot of tricks and techniques to get us started!
Learning Objectives
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
