The Rock Cycle

The Rock Cycle


rock cycle diagram

All rocks are made up of minerals. The rock cycle explains the process.

A mineral is defined as a naturally occurring, crystalline solid of definite chemical composition and a characteristic crystal structure.

A rock is any naturally formed, nonliving, firm, and coherent aggregate mass of solid matter that constitutes part of a planet.

(Diagram and description taken from Idaho Museum of Natural History)


rock cycle diagram

(Diagram from


Igneous rock

Igneous rock is formed when magma from the mantle rises up through the Earth’s crust, and cools and solidifies; or when lava on the Earth’s surface cools and solidifies. Igneous rocks are primarily created with heat.

Found in igneous rock: The quartzes (including amethyst, citrine and ametrine), the garnets, moonstone, apatite, diamond, spinel, tanzanite, tourmaline, topaz and zircon.

Rock crystal (quartz) cut like diamonds.


Metamorphic rock

Metamorphic rock is formed when intense underground heat or pressure alters the existing atomic structures of minerals within rocks, and transforms them into other minerals. In essence, metamorphic rocks are created when heat and pressure change existing minerals into something new.

Found in Metamorphic rock: The beryls (emerald, morganite and aquamarine), jade, lapis lazuli, turquoise, spinel, ruby, sapphire, alexandrite, chrysoberyl and zircon.

1.41ct Emerald0.64ct Aquamarine0.77ct Ruby2.01ct Pink Sapphire0.40ct Alexandrite1.81ct Chrysoberyl Cat's Eye

Sedimentary rock

Sedimentary rock is formed when rock is worn down and the fragments are carried by water or the wind, and these sediments are finally compressed together over time.

Found in Sedimentary rock: Jasper, malachite, opal and zircon


The Gem Museum presents The Rock Cycle

rock cycle
The Rock Cycle set up at The Gem Musuem


The Gem Museum is set up to educate visitors on the story of “Mine to Market”. The very beginning of understanding gemstones is to learn about the rock cycle that is a very essential part of the formation of gemstones.

Come and visit us if you are in Singapore! We are opened Monday to Friday, 12pm to 5pm. Admission is free!


References / Further reading:

The Rock Cycle – 34 Kiwis

What is the Rock Cycle? – Idaho Museum of Natural History

Gem formation – International Gem Society

Where did those gemstones come from – ThermoFisher Scientific

Gemstone Formation in Earth’s Crust

Gemstone in Earth’s Crust

A raw crystal held up to the sunlight, Spinel surrounded by corundum (Vietnam).



Twin Spinel gemstone
Looking at a piece of twin spinel, Northern Vietnam.





LEFT: Alexandrite cut and polished. | RIGHT: Alexandrite in the rough.

(Photos from Gemological Institute of America)




LEFT: Sapphire cut and polished. | RIGHT: Sapphire in the rough.

(Photos from Gemological Institute of America)



emerald gemstone → 


LEFT: Emerald cut and polished. | RIGHT: Emerald in the rough.

(Photos from Gemological Institute of America)





LEFT: Ruby cut and polished. | RIGHT: Ruby in the rough.

(Photos from Gemological Institute of America)


Coco Chanel wanted to “cover women with constellations”. Like stars that pattern the night with light, jewels adorn the woman. But before being fashioned into jewellery, a gemstone is usually first a mineral (a naturally-occurring, inorganic solid with a definite chemical composition and an ordered atomic arrangement) formed by geological processes in the Earth’s crust.


Emeralds, for instance, are formed of the mineral Beryl, a chemical compound containing beryllium, aluminium, silicon and oxygen. Its colour comes from additional traces of chromium and vanadium, but different trace elements will produce different colours, allowing the mineral Beryl to form semi-precious stones such as Aquamarine.  


Rubies are formed of the mineral Corundum, and its red colour comes from traces of chromium. Sapphires are also formed of Corundum, and can come in different colours depending on its trace mixtures of iron, titanium, and chromium.


A single rock can be composed of different minerals. From rocks, mineral crystals are mined, cut and polished into precious or semiprecious gems.


How do minerals form in the Earth?

The International Gem Society has a very comprehensive article on how minerals form. In summary, minerals crystallise when conditions of temperature (heat), pressure and time to grow are right, and when there is space to grow.


Heat and Pressure determine the type of mineral formed.

Some minerals (such as Quartz – below left) require very little heat and pressure to form, and will melt or break down under great heat and pressure.

Other minerals (such as Pyrite– below right) need a lot of heat and pressure to form, because at low temperatures, its raw materials can stay mixed up with other minerals’ raw materials.

(Photo from American Museum of Natural History)


How large a crystal you get is affected by Time.

The more time there is for the crystal to grow, the larger it will be, because minerals have an ordered atomic arrangement and it takes time for atoms to be ordered. Since ions are more mobile in water, the presence of water can help accelerate the mineral growing process.


The earth is like a beautiful bride who needs no manmade jewels to heighten her loveliness.  – Kahlil Gibran


(Rock Cycle Diagram from The Geological Society)

There are 4 main processes by which gems form

(Information from the International Gem Society):

  • Molten rock & associated fluids
  • Metamorphism
  • Surface water
  • Gems formed in the earth’s mantle


Molten rock & associated fluids

(Magma crystallisation, Gas crystallisation, Hydrothermal, Pegmatites)

Lava spews out of a fissure in the Virunga mountains

(Photo by Chris Johns, taken from National Geographic)

A river of molten lava

(Photo by Carsten Peter, taken from National Geographic)


Magma crystallisation

Most minerals found in the rocks around us are formed when molten rock (or magma) rises up through the Earth’s crust due to volcanic eruptions or by heat currents that keep the magma in constant motion.


As the hot magma cools, minerals crystallise.

    • If the cooling process is extremely rapid (seconds), no crystals will form, resulting in volcanic glass (not composed of minerals). However, over millions of years, the volcanic glass may crystallise.
    • If the cooling process is rapid (minutes, hours, days, or years), the components of the minerals will not have time to be ordered, and the crystals formed will be small (less than 1mm), resulting in a fine-grained rock.
    • If the cooling process is slow (decades to millions of years), the crystals formed will be large.


During a volcanic eruption, when there is a rapid drop in pressure, gas bubbles can form in the rising magma (Imagine popping a cork from a champagne bottle.) Sometimes these gas bubbles contain a high concentration of certain elements. If the right conditions of heat, pressure and time exist, minerals will crystallise.



When water (e.g. Rain) seeps down through the soil and meets with rising magma, hydrothermal fluids are formed. Such hydrothermal fluids continue flowing through fractures in the Earth’s crust, dissolving minerals along the way. When these mineral-rich hydrothermal fluids cool in “veins” and the right conditions of heat, pressure and time exist, minerals will crystallise.



When volatile-rich magma cools in cavities and the right conditions of heat, pressure and time exist, minerals will crystallise.


Metamorphism – when minerals form from other minerals

(Contact, Regional)

The Andes mountains, formed when the Nazca plate subducted under the South American plate

(Photo by Peter Essick, taken from National Geographic)


Contact metamorphism

When magma forces its way into an existing rock formation, the intense heat breaks down existing rocks and causes minerals to re-crystallise into more stable forms.


Regional metamorphism

Intense heat and pressure arises when tectonic plates below the Earth are shoved toward each other, forcing one on top of the other (This is how mountains form). As the temperature approaches the melting point of the rock, the minerals become unstable. Over millions of years, they change into new varieties.


Surface water

When rainwater flows through the Earth, it deposits the minerals that are dissolved in it along the way into cracks in the existing rocks. Such deposits then lead to the formation of petrified wood, fossils and new minerals.


Gems formed in the Earth’s mantle

Further underground below the Earth’s crust is the Earth’s mantle. While most gemstones form in the Earth’s crust, some gems do form in the mantle, amongst which are diamonds and peridots. Read more about how they form here.

Colourful mineral deposits in the Earth’s landscape

(Photo by Thinkstock/Corbis, taken from National Geographic)


Gypsum formations that mimic flowers found in Mammoth Cave in Kentucky

(The gypsum precipitates out of water in the cave, creating these subterranean forms over time)

(Photo by Tom Uhlman/Alamy, taken from National Geographic)


References / Further reading:

Story of a gem – Gemological institute of America

What is a gem? – University of Berkeley

What is a mineral? – Oxford University Museum of Natural History

Minerals and Gems – National Geographic

Mineral forming environments – American Museum of Natural History

Formation of minerals – BC open textbooks

FAQ Mineral formation – University of California

Gem formation – International Gem Society

Plate tectonics — National Geographic


Assessing Value of Gems (Part 1)

Assessing Value of Gems

Natural Gems and minerals (and jewellery of course!) are beautiful, intriguing and rare. We all know they hold a certain value and is something that everyone would like to own a piece.

So how do we know what value and how to value a beautiful piece of gem?

First of all, assessing value of gems requires a lot of experience. Experience can come in the form of buying and selling, or learning from the books and history of previous transactions, for example in auctions.

In this 3-part series of assessing value of gems, we will not be showing exactly HOW to assess value. But we will give you an insight on the factors to understand and consider, before you begin to assess the value of the gems.

What gives gems a value? What makes gems valuable?

Gems are valuable because of the following factors:

  • Beauty
  • Rarity
  • Durability
  • Demand
  • Tradition
  • Portability


To begin, beauty is the first attribute that we can see with our naked eyes. For most part, the 4Cs have been a big contributor for understanding the beauty of a gem. These are: Carat weight, Clarity, Colour and Cut. However, the 4Cs probably applies more to transparent, faceted gems. Other gem materials like jadeite-jade and nephrite-jade has its own unique grading system. Therefore, the beauty of a gem may also be described as the ‘quality’ of a gem.

Assessing value of gems
A set of blue sapphires put together for colour comparison. Colour is an important factor when assessing value of gems.


Rarity means uncommon, or unusual. Diamonds are rare because the yield of mining production is very low. For every 5carat total weight of diamonds mined, approximately 300 tons of ore needs to be processed. Similarly for rubies and sapphires, in many mining countries, the mining technique is still quite manual, although some are semi-automatic. Kashmir sapphires for example, are mined from very harsh conditions. Hence, explaining its rarity.

There are also some gemstones which are rare because of its phenomenal optical effects. In order to achieve perfect chatoyancy (cat’s-eye) or asterism (star), it depends on the rough material as well as the lapidary. When the best of the two comes together, the fashioned gemstone becomes very rare.

assessing value of afghanistan emeralds
Rough Afghanistan emeralds. These emeralds tend to be slightly lighter in colour and not as saturated as those of Columbian emeralds. However, beautiful green pieces are also very hard to come by. The value is in its ‘hard to come by’ factor.



Gemstones are valuable because of its durability. It doesn’t get damaged easily and therefore keeps its quality the same for a very very long time. Therefore, some pieces of gems and jewellery can be kept and passed down from one generation to another. Family heirlooms have very intrinsic value that is very hard to quantify. When assessing value of gemstones, we also will look at how well it has kept its durability, i.e. how well it has been maintain at its highest quality.

Durability involves a few factors: hardness, toughness and stability (to light, heat and chemicals). We will discuss these in the future blog posts.

Meanwhile, we do not want to see chips and scratches on our gems!

assessing value by duarbility
This amethyst has polishing marks on the surface. This is because it has a hardness of only 6.


Assessing value of gemstones to be continued…

We have discussed three reasons why gemstones are valuable. In fact, these factors applies also to diamonds and minerals, except for some variations in the details.

In the second part of this topic, we will continue to discuss on why gemstones are valuable.

The Basics of Understanding Gemstones (Part II)

Understanding Gemstones Part II


Let’s recap the first three categories of gemstones in Part I:

  1. Crystal Systems
  2. Organic Gem Materials
  3. Phenomenal Gems

The next three categories of gem materials are as below:

  1. Rare Gems
  2. Imitation
  3. Synthetic

Rare Gems

Perhaps this can be better described as unusual or uncommon gems. Some examples are like kornerupine and sillimanite. These gems are often not as popular because they either come in small quantities, or they are not as attractive as the others like rubies and sapphires. Nevertheless they are still very beautiful nature’s creations. Other examples shown in the pictures below are some collections we have in The Gem Museum.

This is an old collection we have. Small and fragile.
Crocite, USA. This is another small piece we have that is very fragile and is crumbling apart.
Wulfenite, USA. Wulfenite is a lead molybdate mineral with the formula PbMoO4.



Technically, these should not be described as “gems”. These materials are mainly man-made and artificial materials. The term ‘imitation’ means to ‘simulate’. It could be using a natural material to simulate another natural material of a higher value. An example is using serpentine to imitate a more valuable jadeite. Most of the time, due to the low cost and high consistency in production, glass is the most common material used to imitate many other gemstones. Green glass to imitate jade or emerald, red glass to imitate ruby and blue glass to imitate sapphire.

jade imitation
Dyed quartzite imitating jadeite-jade.
Natural Jadeite-jade.
Serpentine carving that is often mistaken as Jadeite-jade.


Many companies out there are selling synthetic materials, but not explaining clearly to consumers what synthetic really means. The emphasis is always on the fact that synthetic materials have exactly the same physical and chemical properties as the natural counterpart. These materials are considered artificial as they are “lab-grown” and sold in the market for less than half the price most of the time. Synthetic materials can be produced in large quantities at any one time. This includes diamonds. As such, the rarity factor of a ‘gem’ is hardly applicable for these materials. Although they are also beautiful, the value of these materials can never match up to a natural gemstone of the same quality.

natural rubies
A set of natural rubies put together to compare its colour quality.
synthetic rubies
These are synthetic rubies that have the same chemical and physical properties as natural rubies.

The Basics of Understanding Gemstones (Part 1)

The Definition of “Gemmology”.

noun: gemology
  1. the study of precious stones.

Our Mission…

The Gem Museum’s mission is to help people appreciate the value of gems through understanding quality and learning about authenticity. Therefore in this two part series, we would like to introduce to you 6 categories of gems and gem materials.

1) Crystal Systems

First of all, here is a need to first understand crystals, in order to understand the structural and optical properties of gemstones. It is from here that you can identify the gemstones. Most miners, for example, in Thailand, Sri Lanka or Myanmar, they do not have formal education. They grow up in mines and start mining for gems at a very young age. However, they could probably identify the rough gem materials, simply based on their observations of structural and optical properties of gems.

gemstone crystals
An overview of the 7 Crystal systems
cubic system
Examples of cubic system: Diamond, spinel, garnet, fluorite
Aquamarine is in the Hexagonal crystal system.

2) Organic Gem Materials

Most people do not realise that these are considered gems too. One of the classification of gem materials is ‘organic’ gems. Organic gems mean that the gem materials was formed through process involving life organisms and some examples are amber, pearls, and even petrified wood.

Fossilized Coral

3) Phenomenal Gems

Finally, in this post, we will talk about some gemstones with special optical effects. Phenomenal Gems have very unusual optical properties. Not all gem materials exhibit optical phenomenal. The optical phenomenal of a gem material could be due to internal reflection of the inclusions, such as cat’s-eye. Another possibility is the structural arrangement of the material, such as moonstones that give the moonlight sheen, described as “Adularescence”. Most of all, our gem museum has a unique collection of double stars and we are still in the midst of searching for more double stars too!

star sapphire
A star sapphire set in a ring.
Labradorite exhibits an optical effect that is due to interference caused by the layering of the material.

In conclusion, there are many ways to categorise and classify gem materials. Hence, look out for the next part of this blog, so that you can understand more about gems and gemstone materials!

Celebrating our 2nd Anniversary

“No valleys, no mountaintops.” – B.C. Forbes

On 1 June 2017, we celebrated The Gem Museum’s 2nd Anniversary. We are grateful to everyone who has been supporting us in various ways since we opened in 2015.

For the purpose of our 2nd anniversary, we have invited the press and media from various publishers in Singapore and around the region to grace a special event on 10 unique diamonds.

10 unique diamonds showcased on our anniversary
Setup for the 10 unique diamonds

Before the 10 unique diamonds were presented, we brought our guests through a journey from “Mine to Market”. Special thanks to Mr. Tay Thye Sun for contributing many of the gems and rock samples to educate about geology and gem formation, the first section of the museum. Here, we have a “Rock Garden”, featuring some of our collections from different countries such as Australia, China, Indonesia and Madagascar.

Geology & Gem Formation
Geology & Gem Formation

Of the 10 unique diamonds, the most special diamond is a 1.5ct heart-shaped Chameleon Diamond. We also want to give a special shoutout to our friends from Hong Kong, who are avid diamond collectors, Mr. Si and family. Without which we would not have such great fun showing a beautiful piece of diamond to our guests.

Chameleon Diamond
Heart-shaped chameleon diamond

At the end of the event, there was good interaction with questions and answers. Some of the questions include “How does one become a gemmologist?”, “Which is the most valuable gemstone or diamonds we have seen?” etc. It was a great time of sharing knowledge and experiences.

exhibit demonstration
Mr. Tay Kunming speaking with the guests

Once again, we sincerely thank everyone who had helped us and supported us in one way or another throughout the last two years.

The next exciting event coming up would be the “Moons & Stars” exhibition that we will be setting up during the Singapore’s Night Festival along the Bras Basah and Bugis (BBB) district. Do look out for updates in the next few months!