Rocks and Minerals on Earth

Introduction:

Have you ever thought of the composition of rocks? Why are there so many different colors, shapes, and textures of rocks?

A rock is a solid and hard object made up of different minerals.

What is a Mineral?

• Several common substances found on Earth, like table salt and the graphite present in pencil, consist of minerals.
• Minerals are non-living natural materials that makeup rocks. In fact, minerals can be thought of as the basic components of rocks.

Quartz is available in a variety of colors, including rose, white, and purple.

It is also possible for it to be colorless. The second very common mineral is quartz.

• Every type of mineral on the planet is made up of the same element or combination of elements. Remember that elements are the building blocks of all matter.
• Carbon is always present in the mineral graphite. Sodium and chlorine are always present in table salt. Each mineral has its own chemical composition.
• Each mineral has a distinct crystal shape. Some crystal shapes are similar to cubes. Some are shaped like hexagons. The crystal shape of a mineral is determined by the orderly arrangement of its atoms.

• Hornblende is a type of mineral found in granite. Hornblende is commonly found as black specks in granite. Hornblende does not shine as brightly as mica.

Over 3,000 different minerals have been identified by scientists. There are only about 30 of these in rocks. These minerals are referred to as rock-forming minerals.

Mica can be easily peeled into thin sheets. Mica is typically either black or clear.

It could be brown or even purple in color.

Feldspar is a mineral that accounts for roughly half of the Earth’s crust. Feldspar comes in a range of colors.

Identification of Minerals

• Minerals are distinguished by their numerous physical properties. Color is one of these properties.
•  Only color cannot be used to identify minerals.
• Quartz and feldspar, for example, can both be white. They can both be different colors as well.
• To identify a mineral, properties other than color must be used.

Luster

• The property of luster is used to recognize minerals.
• Luster explains how light reflects off a mineral’s surface. Some minerals have a metallic luster or shine.
• Other minerals may be dull or non-lustrous. Others may be glassy, pearly, or greasy in appearance.

Pyrite, also called “fool’s gold,” has a metallic luster.

Cleavage

• Cleavage is the process by which a mineral is split. This property is used to identify minerals.
• Some minerals, such as mica, split into thin sheets along a flat surface.
• Some minerals, such as calcite, split along flat surfaces, forming a flattened cube-like shape.
• Other minerals, such as quartz, split apart unevenly.

Streak

• A mineral’s streak can also be used to identify it. The color of the powder left when a mineral is scratched along a white tile, known as a streak plate, is called a streak.
• Some minerals leave a streak that matches the color of the mineral. Other minerals leave a different color streak.
• For a given mineral, the streak always remains the same. Calcite, for example, can be white or colorless. Its streak, however, is always the same color, white.

Hardness

• The ability of a mineral to scratch or be scratched by another mineral is referred to as hardness. The Mohs hardness scale illustrates the hardness of several common minerals.
• There are numerous minerals for each hardness level.
• The hardest mineral is diamond, which has a hardness rating of 10 on the scale. Talc, with a hardness of one on the scale, is one of the softest minerals.
• Any mineral can scratch any other mineral with a higher or equal number.
• Quartz, for example, scratches any mineral with a hardness that is less than or equal to 7. However, quartz’s surface can only be scratched by minerals with a hardness of greater than 7.

You can also determine the hardness of minerals using common household items.

• Gypsum and talc are easily scratched by your fingernail.
• Calcite, gypsum, and talc can all be scratched with a penny.
• Any mineral with a hardness of less than 5.5 can be scratched by a glass.
• Any mineral with a hardness of less than 6.5 can be scratched with a steel nail.
• Any mineral with a hardness of less than 4.5 can be scratched with an iron nail.

Uses of Minerals

Many of the things you see or use on a daily basis contain minerals.

• Quartz is used in the production of glass.
• Fluoride from fluorite is present in your toothpaste.
• Drywall, which is used to build interior walls, is made of gypsum.
• Talc or mica may be present in the paint on the walls of your classroom.
• Copper is used in the manufacture of electrical wires and cooking utensils.

Gems are another type of useful mineral.

• Diamonds or rubies are used in rings or other jewelry.
• Diamonds are used in cutting tools.
• Diamonds, rubies, and emeralds are just a few of the gems extracted from the Earth’s crust.

Many of the minerals we use are derived from ores.

Ores are rocks that are mined [dug] for their useful minerals.

• Galena is a lead-containing ore.
• Hematite is an iron-containing ore.
• Bauxite is an aluminum-containing ore.