minerals

The Earth is composed of rocks. Rocks are aggregates of minerals. So minerals are the basic building blocks of the Earth.  Currently, there are over 4,000 different minerals known and dozens of new minerals are discovered each year. We use things made from rocks and minerals every day. Without them, there would be no cars, trains, or planes. You wouldn't be able to clean your teeth or wash your clothes. Clocks, watches and jewelry, tin cans and aluminum foil are all minerals. So read on to find out more about the minerals!

Learning Objectives

• What is a mineral?
• Difference between mineral and rock.
• Physical properties of minerals.
• Types of minerals.
• Facts about the mineral.

What Is A Mineral?

Minerals are solid substances that occur naturally. They can be made from a single element (like gold or copper) or from a combination of elements. The Earth is made up of thousands of different minerals.

To be classified as a "mineral," a substance must meet five requirements:

1. It should be naturally occurring. This means that it forms in nature on its own without the aid of humans. For example, steel is not a mineral instead it is an alloy produced by humans. 
2. It should be inorganic. This means that the substance is not made by an organism. For instance, wood and pearls are made by organisms and thus are not minerals.
3. It should be solid, not liquid or gas, at standard temperature and pressure.
4. It should have a definite chemical composition. This means that every time we see a mineral, it has the same chemical composition that can be expressed by a chemical formula. For example, the mineral halite, also known as rock salt when mined, has a sodium chloride chemical composition. It is made up of atoms of sodium and chlorine. 
5. It should have a characteristic crystalline structure or an ordered internal structure. This means that the atoms in a mineral are arranged in a systematic and repeating pattern. For example, the mineral halite is composed of an equal ratio of sodium and chlorine atoms arranged in a cubic pattern.

Halite mineral crystals

So, we can say a mineral is a naturally occurring inorganic solid with definite chemical composition and an ordered atomic arrangement. 

The study of minerals is known as mineralogy. The scientist who studies minerals, their composition, uses, and properties is known as a mineralogist.

What is the difference between a mineral and a rock? 

• Minerals have a specific chemical structure that is the same throughout the entire mineral. Their internal structure and chemical composition give minerals characteristic physical and chemical properties that provide clues to the identity of the minerals. 
• On the other hand, rocks are composed of a variety of different minerals and are not consistent throughout their structure. 

Physical Properties of Minerals

Color, luster, streak, hardness, cleavage, fracture, specific gravity, and crystal, form are the most useful physical properties for identifying most minerals.

Luster

Luster describes the appearance of a mineral when light is reflected from its surface.

• Minerals with a metallic luster look like metal, such as steel or copper. They are both shiny and opaque.
• Minerals with an earthy luster look like earth or dirt. Like metallic minerals, these are completely opaque but dull.
• Vitreous luster is like that of glass, shiny and translucent to transparent.
• Minerals with a waxy luster look like paraffin, typically translucent but dull.
• While minerals with pearly luster have an appearance similar to a pearl or the inside of an abalone shell – translucent and shiny but with a bit of light refraction, producing a rainbow effect on the surface.

Color

Color is one of the most obvious properties of a mineral but it is often of limited diagnostic value, especially in minerals that are not opaque. While many metallic and earthy minerals have distinctive colors, translucent or transparent minerals can vary widely in color. Quartz, for example, can vary from colorless to white to yellow to gray to pink to purple to black. On the other hand, the colors of some minerals, such as biotite (black) and olivine (olive green) can be distinctive.

Streak

Streak is the color of the mineral in powdered form. Streak shows the true color of the mineral. In large solid form, trace minerals can change their color appearance by reflecting the light in a certain way. Trace minerals have little influence on the reflection of the small powdery particles of the streak. The streak of metallic minerals tends to appear dark because the small particles of the streak absorb the light hitting them. Non-metallic particles tend to reflect most of the light so they appear lighter in color or almost white. Because a streak is a more accurate illustration of the mineral’s color, the streak is a more reliable property of minerals than color for identification.

Hardness

Hardness is the resistance of a mineral to scratching or abrasion by other materials. Hardness is determined by scratching the surface of the sample with another mineral or material of known hardness. The standard hardness scale, called Mohs Hardness Scale consists of ten minerals ranked in ascending order of hardness with diamond, the hardest known substance, assigned the number 10.

Mohs Hardness Scale

1. Talc

2. Gypsum

3. Calcite

4. Fluroite

5. Apatite

6. Feldspar

7. Quartz

8. Topaz

9. Corundum

10. Diamond

Cleavage and fracture

Cleavage and Fracture - The way in which a mineral breaks is determined by the arrangement of its atoms and the strength of the chemical bonds holding them together. Because these properties are unique to the mineral, careful observation of broken surfaces may aid in mineral identification. A mineral that exhibits cleavage consistently breaks, or cleaves, along parallel flat surfaces, called cleavage planes. A mineral fractures if it breaks along random, irregular surfaces. Some minerals break only by fracturing, while others both cleave and fracture.

Crystal form

A crystal is a solid, homogeneous, orderly array of atoms and may be nearly any size.

Specific gravity

The specific gravity measures the density of the mineral. It is measured in comparison to the water where water has a specific gravity of 1. For example, pyrite has a specific gravity of 5 and quartz has a specific gravity of 2.7. The specific gravity of a substance compares its density to that of water. Substances that are denser have higher specific gravity.

Some minerals have unusual properties that can be used for identification. Let's look at some examples. 

Fluorescence - Mineral glows under ultraviolet light. For example, fluorite. 

Magnetism - Mineral is attracted to a magnet. For example, magnetite. 

Effervescence- When mineral is exposed to a weak acid, bubbles are formed. For example, calcite. 

Radioactivity	Mineral gives off radiation that can be measured with Geiger counter	Uraninite
Reactivity	Bubbles form when mineral is exposed to a weak acid	Calcite
Smell	Some minerals have a distinctive smell	Sulfur (smells like rotten eggs)
Taste	Some minerals taste salty	Halite

 

Types of Minerals

There are many different types of minerals, but they are often divided into two groups: silicates and non-silicates.

• Silicates are minerals that contain silicon and oxygen. Over 90% of the earth’s crust is made up of silicates.
• The rest of the minerals are lumped into a group called non-silicates.

Some important non-silicates minerals include:

• Carbonates – Carbonates contain carbonate (CO3) combined with some other element. Calcite is a mineral made from carbonate and calcium.
• Halides – Halides contain a halogen element as the main element. Table salt (NaCl) is a halide mineral made from the halogen chlorine (Cl) and sodium (Na).
• Oxides – Oxides are minerals and the main element is oxygen. Chromite is an oxide mineral made from iron, chromium, and oxygen.
• Sulfides – Sulfides contain sulfur and one or more metals or semi-metals. Pyrite is a sulfide made from iron and sulfur.

Native elements such as copper, gold, diamond, graphite, and sulfur can be thought of as a third group of minerals.

Facts about Mineral

• Scientists who study minerals are called mineralogists.
• Around 99% of the minerals in the Earth’s crust are made up of eight elements including oxygen, silicon, aluminum, iron, calcium, sodium, potassium, and magnesium.
• Common minerals include quartz, feldspar, bauxite, cobalt, talc, and pyrite.

• Some minerals have a different colored streak than the color of their body.
• A gem is a piece of rare minerals such as diamond, emerald, or sapphire that is cut and polished to shine.

• Certain minerals are needed by our bodies so we can grow healthy and strong.