Properties of Minerals

In this lesson, students analyze the kinds of atoms that make up different substances and figure out the way those atoms combine to determine the phenomena exhibited in the substance’s properties.

• Minerals are naturally occurring, inorganic substances that have an orderly crystal structure. 
• Minerals are made up of combinations of different elements. 
• Scientists use different property tests to identify unknown rocks and minerals. This is useful because scientists have discovered more than 3,000 minerals. 
• Rocks are a mixture of minerals.
  
  

• How do we know that minerals are made up of atoms?
• Why do scientists use more than one test to identify a mineral?
• Why is it useful for scientists to know that blue diamonds are phosphorescent?
• How is the property of hardness useful to scientists?
• How can different diamonds be described using the property of luster?
  
  

Misconception: Weathering and erosion refer to the same process.

Fact: Weathering and erosion are two different processes that often work closely together (weathering breaks down rocks and erosion transports the sediment).

Mineral : a naturally occurring, inorganic solid with a crystal structure

Rocks : mixed mineral matter that makes up the surface of Earth and other terrestrial objects

System : a set of connected, interacting parts that form a more complex whole

The Hope Diamond

A museum in Washington, D.C., holds the world’s largest deep blue diamond. This 45-carat blue diamond is the size of a walnut. It is called the Hope Diamond.

The Hope Diamond has long fascinated humans. More than 100 million people have visited the museum to see the diamond. It was first discovered in India in the 1600s, but its history goes back far beyond that. Scientists believe it is at least 1 billion years old and was formed so deep inside Earth that humans cannot travel there.

How Diamonds Form

All diamonds are formed deep within Earth, at least 161 kilometers (100 miles) below the surface. They can only form under tremendous heat and pressure. This heat and pressure are a result of Earth’s structure.

The center of Earth is a solid ball of metal iron and nickel. It is called the inner core. The core is 7,000 degrees Celsius, hotter than the surface of the sun. The outer core wraps around the inner core and is made of liquid iron and nickel.

The mantle is located around the outer core. The mantle is Earth’s thickest layer. Imagine an apple. The core of the apple is like Earth’s core, and the fleshy part that you eat is like the mantle. Earth’s mantle is an ocean of semi-solid rock called magma. It is here where diamonds are formed.

Earth’s “skin” is its crust. The solid crust is the coolest layer of the planet that forms the continents and holds the oceans.

Diamonds Are Minerals

Diamonds are made mostly of a single element—carbon. The heat and pressure of Earth’s interior caused the carbon atoms to join together in a way that resulted in the unique physical properties of diamonds.

Diamonds are minerals. Scientists have found more than 3,000 minerals, made up of different combinations of elements.

All minerals are naturally occurring, which means they are not made by humans. They would exist on Earth without people. Minerals are also inorganic because they are not the product of something that is living or was once alive. (Leaves and shells are organic because they come from something that was once alive.)

They also have a definite chemical composition. This means that every mineral is made up of the same kind and number of atoms. For example, diamond can always be described by the chemical formula of C since it is made of carbon atoms. Lastly, minerals have an orderly crystal structure. This means their atoms are neatly organized to form a repeating pattern. 

Identifying Minerals

One of the reasons that people are drawn to the Hope Diamond is its color. Blue diamonds are very rare. They are blue because they have traces of the element boron combined with the carbon atoms. Diamonds come in many different colors, including red, yellow, green, purple, and brown. Color is one property that scientists use to identify minerals.

In addition to color, there are many other property tests that scientists can do to identify a mineral. For example, scientists were fascinated to discover that the Hope Diamond gives off a fiery red glow after it has been exposed to ultraviolet (UV) light. This is called phosphorescence. Scientists have learned that all natural blue diamonds glow red for about five minutes after being exposed to UV light. However, blue diamonds created by humans give off different colors. Because of this, phosphorescence helps scientists determine whether a blue diamond is real or fake. Other diamonds do not phosphoresce. Instead, they fluoresce, which means they give off light only as long as UV light is shined on them.

 

In this lesson, students figure out the composition of rocks and minerals by experimenting on the physical phenomena exhibited by different samples to determine if the physical properties of a sample can be used to identify it. Then, they use the data from their investigation to figure out why scientists use multiple properties to identify minerals. Students use their knowledge of atoms, elements, and minerals, to evaluate why different rocks and minerals have unique sets of properties.