Minerals Text Book Pages : 44 - 53

So what is a mineral? A naturally occurring, inorganic solid that has a crystal structure and a definite chemical composition. What are the characteristics of all minerals?

Do you know Mineral’s Characteristics

To Be a Mineral a Substance All Five Characteristics Must Have All Five Characteristics Now I See Crystal Clear! Naturally Occurring Inorganic (Was Never Alive) Solid Crystal Structure Chemical Composition

Must be formed by processes in the natural world. Naturally Occurring Must be formed by processes in the natural world. Mineral Quartz forms naturally as molten material cools and hardens deep beneath Earth’s surface.

NO Are man made materials like Plastic, brick, glass, and steel can be called minerals? NO

A mineral can not form from organic materials (living things). Mineral has to be Inorganic Remember: A mineral can not form from organic materials (living things). Is coal a mineral? No, it comes from the remains of plants that lived millions of years ago.

Has definite volume and shape Mineral is always a solid Has definite volume and shape Mineral has a crystal structure A solid in which the atoms are arranged in a pattern that repeats again and again. Has flat sides, called faces, that meets at sharp edges and corners. Like a snowflake pattern or rock candy.

Always contains certain element in definite proportions. Mineral has a Definite Composition Always contains certain element in definite proportions. Quartz has one atom of silicon for every two atoms of oxygen.

Rarely is a mineral identified by a single property. Identifying Minerals Remember!: Rarely is a mineral identified by a single property. These properties need to be considered together to correctly identify a mineral.

Of the almost 4000 known minerals, only about 30 are common. The most common are: quartz, feldspar, mica, and calcite.

Fact: Over 60% of the Earth’s crust is made up of the family of minerals known as feldspar!

To be able to identify these and other minerals, we need to look at the properties used to separate and distinguish these minerals.

Color Color is the most easily observed mineral property and the least useful! Mineral azurite is always blue. Mineral malachite is always green.

Many minerals have a similar color.

Color Caution: Many minerals have colors due to impurities, or they can change colors in various circumstances.

Color For example, pure quartz is colorless or white, impurities can make the mineral rose, purple or pink!

Streak Streak of a mineral is the color of its powder when rubbed on an unglazed white (porcelain) tile.

The streak is often not the same color as the mineral. A mineral’s color may vary, but the streak rarely will! Mineral sulfur has yellow color, but produces streak of white color on black tile.

Streak For example, Calcite occurs in many different colors, shapes, and varieties. But every single variety of Calcite has a white streak. A streak is useful in distinguishing two minerals with the same color but different streak.

Streak Minerals, which streak very light colors, can be easily identified on black streak plate.

Notice the difference between these two minerals? Luster The way a mineral reflects light from its surface. Notice the difference between these two minerals?

Luster The mineral on the left has a metallic luster, the one on the right, a nonmetallic luster. Galena Quartz

Luster Glassy luster Pearly luster Malachite Topaz Pearl Silky luster

Other terms that might be used include greasy, dull, and earthy. Can you tell which of these has an earthy luster and which has a vitreous luster? Were you Right? Vitreous Earthy

The hardness of a mineral is it’s resistance to being scratched. Diamond is the hardest of all minerals, and talc is the softest.

Friedrich Mohs devised a hardness scale. In this scale, ten well known minerals are given numbers from one to ten. Lets take a look at the ten minerals used and some of the simple tests.

Hardness

Talc is the softest and has a hardness of 1. A soft pencil lead will scratch talc. Gypsum is a bit harder and has a hardness of 2. A fingernail scratches gypsum.

Hardness Fluorite has a hardness of 4. It can be scratched by an iron or brass nail. Calcite has a hardness of 3. A copper penny just scratches it.

Apatite has a hardness of 5. It can be scratched by a steel knife blade. Feldspar has a hardness of 6. It will scratch a window glass.

Hardness Quartz, with a hardness of 7, is the hardest of the common minerals. It easily scratches hard glass and steel. Topaz has a hardness of 8. It will scratch quartz.

Hardness Diamond with its hardness of 10. It can easily scratch the rest of the minerals. Corundum (left) has a hardness of 9. Corundum will scratch topaz.

Cleavage The cleavage of a mineral is it’s ability to split easily along flat surfaces. Cleavage can even be observed on tiny mineral grains making it a very useful property!

Cleavage Mica is probably the best example as it splits into thin sheets. It is said to have one perfect cleavage.

Cleavage Feldspar splits readily in two directions, always at or near right angles.

Calcite and galena cleave in three directions. Cleavage Calcite and galena cleave in three directions. They are said to have three good cleavages.

Not all minerals show cleavage. Fracture Not all minerals show cleavage. Those that don’t break along cleavage surfaces are said to have fracture. Minerals break in irregular way.

Cleavage or Fracture Mica Quartz Copper Cleavage Cleavage Fracture

Most mineral grains that are found in rocks, lack the room to grow. Crystal Shapes Crystal shape can be a useful property to identify minerals if the minerals have had the time and space to form crystals. Most mineral grains that are found in rocks, lack the room to grow.

Pure gold can have a specific gravity as high as 19.3! Specific gravity tells you how many times as dense as water the mineral is. Pure gold can have a specific gravity as high as 19.3!

Calcite is calcium carbonate, CaCO3. Acid Test Calcite is calcium carbonate, CaCO3. If a drop of weak hydrochloric acid is placed on calcite, the acid bubbles as carbon dioxide is released.

Other Special Properties Magnetic Malleable Radioactive Flourescence Taste

Can you think of a mineral that might be shaped or hammered? Malleable or Ductile Minerals that can be hammered thin or shaped are said to show these properties. Can you think of a mineral that might be shaped or hammered?

Gold would be a perfect example!

Magnetic Some minerals that contain Iron, are magnetic and can be picked up by a magnet.

This is the state of glowing while under a ultraviolet light. Fluorescence This is the state of glowing while under a ultraviolet light. Some minerals even glow once the light is turned off!

Some minerals, such as this uraninite, are radioactive. They give off subatomic particles that will activate a Geiger counter.

Halite (rock salt) can be identified by its taste. This practice is not recommended!

Are you ready to classify some minerals?