Introduction
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
Resources
http://www.minerals.net/gemstone/sapphire_gemstone.aspx
https://www.jewelsforme.com/sapphire-meaning
http://www.extremescience.com/sapphires.htm
https://www.gemsociety.org/article/lab-grown-sapphires/
https://www.britannica.com/topic/Verneuil-process
http://www.gia.edu/sapphire-history-lore
http://www.chemspider.com/Chemical-Structure.8164808.html?rid=02eca630-7c75-4d43-ba0b-a5a554104c6c
http://asiangemny.com/sapphire-formation
https://en.wikipedia.org/wiki/Feldspathoid
https://en.wikipedia.org/wiki/Silicate_minerals#Tectosilicates
www.webexhibits.org/causesofcolor/8.html
https://en.wikipedia.org/wiki/Oxyhydrogen
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).