Properties of Minerals

Properties of Minerals

Middle School

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Learning Objectives

• Define a mineral based on its five key characteristics.

• Describe the physical properties used to identify minerals, such as hardness, luster, and streak.

• Explain how the internal arrangement of atoms determines a mineral's properties.

• Use the Mohs hardness scale to compare the hardness of different minerals.

Key Vocabulary

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Mineral

A naturally occurring, inorganic solid with a definite chemical makeup and crystal structure.

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Luster

Describes how light reflects from a mineral's surface, such as metallic or non-metallic.

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Cleavage

A mineral's tendency to break along flat planes, creating smooth surfaces.

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Hardness

A measure of a mineral's resistance to scratching, often tested using the Mohs scale.

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Streak

The color of the powder a mineral leaves when it is scraped across a hard surface.

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What Makes a Material a Mineral?

• A mineral is a solid material formed through a natural process.

• It must be naturally occurring, meaning it is not made by humans.

• It is inorganic, so it does not come from living things.

• It must be a solid, not a liquid or gas like water.

• Its atoms have a repeating pattern, which is called a crystal structure.

• It has a definite chemical composition, like a recipe with exact ingredients.

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Multiple Choice

Which of the following is NOT a required characteristic for a substance to be classified as a mineral?

• It must be formed by natural processes.

• It must be made from something that was once living.

• It must have a repeating pattern of atoms.

• It must be a solid at room temperature.

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Crystal Structure and Composition

Diamond

• ​It is made entirely of carbon atoms, arranged in a strong network.

• ​​The atoms are bonded together strongly in all three directions.

• ​This structure makes diamonds extremely hard, the hardest natural substance on Earth.

Graphite

• ​It is also made entirely of carbon atoms, just like diamond.

• ​​The atoms bond to form layers with very weak connections between them.

• ​These layers can easily slip past one another, making graphite very soft.

Multiple Choice

Why is diamond extremely hard while graphite is very soft, even though both are made of pure carbon?

• Because diamond has a more complex chemical composition.

• Because diamond is made by natural processes and graphite is not.

• Because of the way their carbon atoms are arranged.

• Because diamond is a mineral and graphite is not.

Visual Properties for Identification

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Color

• ​Color refers to the outside appearance of the mineral.

• ​​It is often unreliable for identifying a mineral sample.

• ​Some minerals like quartz can come in many different colors.

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Luster

• ​Luster describes how light reflects from a mineral's surface.

• ​​It can be shiny like metal, which is called metallic.

• ​It can be dull or glassy, called non-metallic.

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Streak

• ​Streak is the color of a mineral in its powder form.

• ​​You see it by scraping the mineral on a hard plate.

• ​Streak is more reliable for identification than the mineral's color.

Multiple Choice

Which property is described as the reflection of light off a mineral's surface, being either metallic or non-metallic?

• Luster

• Cleavage

• Streak

• Color

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Structural Properties: Cleavage & Fracture

Cleavage

• A mineral's cleavage is its tendency to break along flat, smooth planes.

• This breakage happens in areas where the bonds between atoms are the weakest.

• This process results in broken surfaces that look flat and very smooth.

Fracture

• Fracture is the pattern a mineral shows when it breaks in irregular ways.

• This type of break does not happen along any of the cleavage planes.

• The broken surface can be described as jagged, irregular, or smoothly curved.

Multiple Choice

What is the key difference between cleavage and fracture?

• Cleavage is an irregular break, while fracture is a break along a smooth, flat plane.

• Cleavage is a break along a smooth, flat plane, while fracture is an irregular break.

• Cleavage is related to hardness, while fracture is related to luster.

• Cleavage describes how a mineral reflects light, while fracture describes its color.

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Mineral Hardness

• Hardness is a mineral's resistance to scratching and helps in its identification.

• ​The Mohs scale ranks minerals from 1 (softest) to 10 (hardest).

• A mineral can scratch any other mineral that has a lower hardness number.

• Talc is the softest mineral with a hardness of 1 (one).

Multiple Choice

According to the Mohs Hardness Scale, which of these minerals is the softest?

• Diamond

• Quartz

• Gypsum

• Talc

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Common Misconceptions About Minerals

Misconception	Correction
Man-made gems are minerals.	Minerals must be naturally occurring, not made in a lab.
All solids are minerals.	A mineral must have a specific crystal structure.
A mineral's color is its most reliable property.	A mineral's streak is a more reliable identifier than its color.

Multiple Choice

Why is streak considered a more reliable property for mineral identification than color?

• The streak color is consistent for a mineral, while its surface color can vary.

• All minerals have a unique streak color, but many share the same surface color.

• Streak is easier to observe than the color of the mineral.

• Streak measures hardness, while color only describes appearance.

Multiple Choice

A mineral is observed to break apart, leaving smooth, flat surfaces. Which physical property does this demonstrate?

• Cleavage

• Hardness

• Luster

• Fracture

Multiple Choice

You find a mineral that can scratch fluorite (hardness 4) but cannot scratch quartz (hardness 7). What is the possible hardness range for this mineral on the Mohs scale?

• Between 4 and 7

• Exactly 5.5

• Greater than 7

• Less than 4

Multiple Choice

Diamond and graphite are both made from carbon atoms. Why is diamond one of the hardest substances, while graphite is very soft?

• Diamond is a natural substance, while graphite is man-made.

• The way the carbon atoms are arranged is different in diamond and graphite.

• Diamond's atoms are packed closer together, but the arrangement doesn't matter.

• Diamond and graphite are made of different types of atoms.

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Summary

• A mineral is solid, natural, inorganic, and has a specific crystal structure.

• A mineral's properties are determined by the internal arrangement of its atoms.

• Key identification properties include luster, streak, cleavage, fracture, and hardness (Mohs scale).

• Streak and cleavage are often more reliable for identification than surface color.

Poll

On a scale of 1-4, how confident are you about the properties of minerals covered in today's review?

• 1

• 2

• 3

• 4