The Chemistry of Sapphires

Introduction

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I chose to do the chemistry of sapphires because my great-grandfather faceted stones, and I am very fortunate to have one of the sapphire rings that he made.  The ring was made over 50 years ago and used to be my grandma’s.  Sapphires are semi-precious stones that come in all colors except for red, and they are the second hardest gemstone, behind diamonds.  They are formed deep below the surface of the planet and are found all over the world.  Montana, my home state, is famous for its yogo sapphires.

Composition of ...

  • Formula unit is Al2O3

    • Alumina Oxide or Alumina

    • Formula unit for the mineral corundum

  • Iron

    • Fe

  • Titanium

    • Ti


Main Chemicals, Compounds, Components

Naturally occurring sapphires were formed about 150-200 million years ago, and they form in feldspathoid-bearing igneous rocks (Feldspathoids are a group of tectosilicate minerals that make up nearly 75% of the Earth’s crust) that are undersaturated with respect to silica.  Sapphires can also form in recrystallized limestone and in high-grade metamorphic rocks that are poor in silica and rich in aluminum.  Sri Lanka, Burma, U.S. (Montana), Tanzania, Australia, Thailand, Cambodia, and the Kashmir region of India/ Pakistan are all places where sapphires can be found around the world.  


Naturally occurring sapphires are formed by volcanic processes deep below the surface and the high temperature and pressure conditions of metamorphic processes.  As liquid magma cools, minerals dissolve into crystals.  The purest forms of corundum (sapphires are a part of the corundum family) are created by recrystallization of minerals during the metamorphosis of rocks that are of igneous origin.  Sapphires’ colors are formed by mineral impurities that seep into the aluminum oxide.  This is called crystal field or a ligand-field effect.  Blue sapphires get their color from iron and titanium.  


Sapphires that are created in labs are created by using the Verneuil Process (Flame-Fusion Process).  The Verneuil Process is a method for producing synthetic sapphires and rubies.  The artificial sapphires are made by adding 1% rutile (titanium oxide, TiO2) to the starting powder.  This forms boules that are then heat treated at temperatures of 1,100oC-1,500oC.


Chemistry's Role


Sapphires can be formed both naturally and in labs, and chemistry is involved in both ways.  Naturally occurring sapphires are formed deep below Earth’s surface.  They are made out of aluminum oxide, and their blue color is caused by impurities seeping into the aluminum oxide.  Blue sapphires’ color is caused by iron and titanium.  This process of sapphires getting their color is called intervalence charge transfer or cooperative charge transfer.  Intervalence charge transfer is the transfer of an electron from one transition-metal ion to another.  


Artificial sapphires also contain aluminum oxide, and they are created by the Verneuil Process.  These sapphires are made from boules, a mass of alumina with the same physical and chemical properties as corundum, that are heated at temperatures of 1,100oC-1,500oC.


Background Research

The name sapphire comes from the Latin word “saphirus” and the Greek word “sappheiros”, and both of these words mean blue.  Sapphire refers to more than just blue stones.  In fact, sapphires can come in violet, green, yellow, orange, pink, purple, and multiple shades of blue.  These colored sapphires are called fancy sapphires.  Red is the only color that a sapphire cannot be because a red sapphire is a ruby.  


Sapphires are September’s birthstone, and they are the gem of the 5th and 45th anniversaries.  They have been worn by and associated with royalty for centuries.  In fact, sapphires are even known to symbolize nobility.  Kings, specifically Greek and Roman kings, used to wear sapphires to keep them safe from harm.  Sapphires are also believed to have many mystical powers.  People in the middle ages believed that sapphires stopped negative thoughts, and people in ancient Persia believed that when ground up, sapphires were a type of medicine.  They are also believed to ward off sorcery and guard off poisonous creatures.  Sapphires are thought to better one’s connection and awareness of spirit guides and angels.


Resources

http://www.gia.edu/sapphire

  • What the word sapphire refers to

  • Sapphire's’ hardness and durability

  • Formula Unit

  • What sapphires are made up of

http://www.minerals.net/gemstone/sapphire_gemstone.aspx

  • Different types of sapphires

    • Most valuable

    • Fancy sapphires

  • Sapphires are pleochroic and have color zoning

  • Hexagonal crystal structure

  • Synthesized sapphires

https://www.jewelsforme.com/sapphire-meaning

  • Color is based on the amount of iron and titanium

  • History of sapphires

    • Meaning of name

    • Who has worn them

  • Mythical properties of sapphires

  • Heat treatments for improving color

  • Where sapphires are found around the world

http://www.extremescience.com/sapphires.htm

  • Mineral impurities that seep into Aluminum Oxide gives it its color

  • Formed by volcanic processes

  • Process takes millions of years

https://www.gemsociety.org/article/lab-grown-sapphires/

  • Sapphires can be made in labs

  • Two methods for creating artificial sapphires

    • Oldest is flame fusion

    • Czochralski process

  • Lab made sapphires are considered corundum

  • Artificial creation leaves ways of telling the difference

https://www.britannica.com/topic/Verneuil-process

  • Verneuil Process used for making artificial sapphires and rubies

  • Developed in 1902

  • Makes other items besides sapphires

  • Process of making artificial sapphires and rubies

http://www.gia.edu/sapphire-history-lore

  • History and lore of sapphires

http://www.chemspider.com/Chemical-Structure.8164808.html?rid=02eca630-7c75-4d43-ba0b-a5a554104c6c

  • Information on Aluminum Oxide

http://asiangemny.com/sapphire-formation

  • More in depth details on the formation of natural sapphires

https://en.wikipedia.org/wiki/Feldspathoid

  • Information on what Feldspathoid rocks are

https://en.wikipedia.org/wiki/Silicate_minerals#Tectosilicates

  • Explains what Tectosilicates are

www.webexhibits.org/causesofcolor/8.html

  • How natural blue sapphires get their color

https://en.wikipedia.org/wiki/Oxyhydrogen

  • Explains what oxyhydrogen and oxyhydrogen torches are


About the Author
Maddie Randak is a junior at Billings Senior High School.  She loves reading, running, and spending time with her family.  Her favorite place is her family cabin on the Boulder River.  There, she loves relaxing, going on walks, and reading.  Maddie is an identical twin, and she and her sister are both huge animal lovers and love to help animals in need.  Although Maddie is unsure of where she wants to attend college and what she wants to do, she knows that her future career will involve STEM (Science Technology Engineering Math).







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