Top 10 Interesting and Fun Facts About Rocks, Minerals, and Crystals

Updated on September 4, 2019
stuff4kids profile image

Amanda is a retired educator with many years of experience teaching children of all ages and abilities in a wide range of contexts.

The earth's crust is made of rocks and minerals
The earth's crust is made of rocks and minerals | Source

1. Rocks

The study of rocks is known as geology. All types of rock fall into one of three categories:

  • igneous
  • sedimentary
  • metamorphic

Let's look at what each of these means in turn.

All rocks are composed of a variety of minerals
All rocks are composed of a variety of minerals | Source

Igneous Rock

Igneous rock starts off deep within the earth as magma (molten rock). The magma rises toward the surface where it may erupt from a volcano, or cool and solidify within the earth's crust.

Igneous rock that erupts from a volcano and reaches the earth's surface is called "extrusive". Igneous rock that solidifies before it reaches the surface is called "intrusive".

The Giant's Causeway in Northern Ireland is formed from basalt, an extrusive igneous rock
The Giant's Causeway in Northern Ireland is formed from basalt, an extrusive igneous rock | Source

Sedimentary Rock

Rocks are weathered into fragments that are carried away by water, wind, and ice. These sediments are laid down in lakes, rivers, sand dunes, and on the sea floor. Over millions of years they are compressed, forming layers of sedimentary rocks.

Ayer's Rock in Australia is made of sandstone which is a sedimentary rock
Ayer's Rock in Australia is made of sandstone which is a sedimentary rock | Source

Metamorphic Rock

Metamorphic Rock is igneous or sedimentary rock that has been changed by heat and/or pressure. Heat may come from rising magma, and pressure may occur when rock is squeezed during the formation of mountains.

The rock underlying this landscape in Northwest Scotland is gneiss, a type of metamorphic rock
The rock underlying this landscape in Northwest Scotland is gneiss, a type of metamorphic rock | Source

2. Geological Timescale

Rocks are dated according to a geological timescale that divides the earth's history into eras, periods, and epochs.

Era
Period
Ma (Million years ago)
Cenozoic
Quarternary
 
 
Holocene (epoch)
0.01
 
Pleistocene (epoch)
2
 
Tertiary
 
 
Pilocene (epoch)
5
 
Miocene (epoch)
25
 
Oligocene (epoch)
38
 
Eocene (epoch)
55
 
Paleocene (epoch)
65
Mesozoic
Cretaceous
144
 
Jurassic
213
 
Triassic
248
Paleozoic
Permian
286
 
Carboniferous
360
 
Devonian
408
 
Silurian
438
 
Ordovician
505
 
Cambrian
590
 
Precambrian (about 7 times longer than all the other periods combined)
4,600 (to the origin of the earth)
A table showing the geological timescale of earth's history divided into eras, periods, and epochs

3. The Rock Cycle

All rocks are constantly passing through a recycling process.

Igneous rocks are weathered away and washed into the oceans. Mineral particles sink into the sea floor where they are compacted into sedimentary rocks. Heat from molten rock changes surrounding sedimentary and igneous rock into metamorphic rock. Molten rock in the magma may rise to the surface where it cools forming new igneous rocks.

A diagram showing the events of the rock cycle
A diagram showing the events of the rock cycle | Source

4. Marvelous Minerals

A mineral is a natural, non-living substance. Examples include gold, silver, gypsum, quartz, and sulfur.

Rock-Forming Minerals

Different combinations of minerals form different kinds of rock. Granite, for example, is composed of three minerals: quartz, feldspar, and mica.

A photograph showing the mineral composition of a slab of granite. The white areas are quartz, the buff-colored parts are feldspar, and the black specs are mica.
A photograph showing the mineral composition of a slab of granite. The white areas are quartz, the buff-colored parts are feldspar, and the black specs are mica. | Source

Ore Minerals

Ore minerals contain metals and about 80 types of pure metal are extracted from them. The ones we most commonly see and use in everyday life are:

  • Rutile, from which we extract titanium. Titanium is a light, strong, flexible metal used in building aircraft.
  • Bauxite, from which we extract aluminium. Aluminium is used in construction and the manufacture of goods such as cans and saucepans.
  • Galena, from which we extract lead. lead is the softest of the common metals and we use it in making batteries and in engineering.
  • Hermatite, from which we extract iron. Iron is used in construction and as an ingredient in making steel.
  • Chalcopyrite, from which we extract copper. Because copper is an excellent conductor it is widely used in electrical applications.
  • Cinnabar, from which we extract mercury. Mercury is liquid at room temperature and is used in making scientific and medical instruments and in the manufacture of drugs and pesticides.

An operative iron ore mine. Ore minerals of every kind are extracted from the earth in vast quantities and used in manufacture and industry
An operative iron ore mine. Ore minerals of every kind are extracted from the earth in vast quantities and used in manufacture and industry | Source

5. Incredible Crystals

Crystals grow from molten minerals, or minerals that are dissolved in liquids, such as water. Of the earth's rocks and minerals, 85% are formed from crystals.

All crystals can be categorized according to their geometrical shape, known as its "system", and its physical hardness plotted on a scale of 1 to 10.

A variety of crystals
A variety of crystals | Source

Crystal Systems

System
Examples
Cubic
Diamond, galena, garnet
Tetragonal
Zircon, rutile, vesuvianite
Hexagonal
Corundum, beryl
Orthorhombic
Sulfur, olivine, topaz
Monoclinic
Malachite, gypsum
Triclinic
Rhondonite, kyanite, turquoise
Table listing the six most common crystal systems with named examples

Measuring Mineral Hardness

The hardness of a mineral is graded on a scale of 1 to 10 devised by the German mineralogist, Freidrich Mohs (1773 to 1839).

Mohs Mineral Hardness Scale

Scale
Example
1
Talc
2
Gypsum
3
Calcite
4
Flourite
5
Apalite
6
Orthoclase
7
Quartz
8
Topaz
9
Corundum
10
Diamond
Table showing Freidrich Mohs' mineral hardness scale with examples

6. Mineral Structure

A mineral's hardness depends on the arrangement of its atoms. Diamonds and graphite are different forms of the same element, carbon, but their hardness varies because of their different internal structures.

Diamonds are the hardest of all minerals. Each atom is strongly bonded to four others, forming a compact, rigid structure.

In graphite, the atoms are arranged in layers that easily slip over each other. This gives graphite its weak structure.

7. Gemstones

Gemstones are minerals valued by humans for their beauty, rarity, and durability. There exist about 100 different types of gemstones. The most valuable include diamonds, emeralds, rubies, and sapphires.

A selection of gemstones
A selection of gemstones | Source

Diamonds

Hardness: 10

System: Cubic

Found in Russia, South Africa, Australia, and Brazil

A diamond
A diamond | Source

Rubies

Hardness: 9

System: Trigonal

Found in India, Thailand, Burma, and Sri Lanka

Rubies are highly prized in the making of jewelry
Rubies are highly prized in the making of jewelry | Source

Emeralds

Hardness: 7 to 8

System: Hexagonal

Found in Russia, USA, Zambia, and Colombia

This necklace has a beautifully formed emerald at its center
This necklace has a beautifully formed emerald at its center | Source

Organic Gemstones

Organic gemstones are those which have a plant or animal origin. They include pearls, shell, jet, and amber.

8. Giant-Size Gems

The largest diamond was called the Cullinan. It was found in Africa in 1905. It weighed the same as a full-grown pineapple.

The largest pearl is called the Pearl of Lao-Tze. It was found in the Philippines in 1934 in the shell of a giant clam. It weighs about the same as a four-month-old baby.

The Cullinan diamond was the largest gemstone ever found.
The Cullinan diamond was the largest gemstone ever found. | Source

9. Carats and Beans

The weight of a gemstone is measured in carats.

1 carat = 0.2 g (0.007 oz)

The term carat comes from the Greek word for carob seed. These little beans were once used as weights.

The purity of gold is also measured in carats. The purest gold is 24 carats.

The mineral measurement "carats" comes from the Greek for carob beans which were once used as weights
The mineral measurement "carats" comes from the Greek for carob beans which were once used as weights | Source

10. Rocking Out

  • More than half all the gold mined returns to earth - as most of it is buried in subterranean bank vaults!
  • The word crystal comes from the Greek word kyros, meaning icy cold. It was once thought that rock crystal was ice that had frozen so hard it would never thaw
  • About one in every thousand oysters and one in every three thousand mussels, has a pearl inside

A Last Word

I hope you've enjoyed these top 10 interesting and fun facts about rocks, minerals, and crystals. Both geology and mineralogy are fascinating subjects which will reward you well for the time you put into studying them. To be a professional geologist you'll need to do well in geography and chemistry at school and then go on to study for a degree in natural sciences. Good luck!

© 2019 Amanda Littlejohn

Comments

Submit a Comment
  • stuff4kids profile imageAUTHOR

    Amanda Littlejohn 

    5 months ago

    Thanks, Kathi. I'm so glad you enjoyed it.

  • Fossillady profile image

    Kathi 

    5 months ago from Saugatuck Michigan

    Great article, lots of good information and photos!

  • stuff4kids profile imageAUTHOR

    Amanda Littlejohn 

    8 months ago

    A Google image search does turn up pictures of it. The problem was finding one which is legal to use for commercial purposes. It's not a very pretty thing, that pearl, as you'll see if you search for it.

  • bdegiulio profile image

    Bill De Giulio 

    8 months ago from Massachusetts

    If you ever do find a picture of it please post it. I had to read that twice, amazing.

  • stuff4kids profile imageAUTHOR

    Amanda Littlejohn 

    8 months ago

    Thanks, Bill.

    I'm glad you enjoyed it. I tried so hard to find a picture of the giant pearl, but it seems impossible.

  • bdegiulio profile image

    Bill De Giulio 

    8 months ago from Massachusetts

    Another interesting hub, Amanda. Thank you for the geology education. This is definitely a fun topic.

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