Difference between revisions of "Alumina"
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| − | '''Alumina''' is the chemical <math>Al_2O_3</math>, or aluminium(III) oxide. It occurs naturally as hexagonal crystals called '''corundum''', the second hardest [[mineral]] on Earth.<ref name=Cairncross>B. Cairncross - ''Field guide to rocks and minerals of Southern Africa'' 2004. ISBN 978-1-86872-985-2 pp. 80-82</ref> Used without qualification, '''aluminium oxide''' usually refers to alumina rather than the other oxides of aluminium. | + | '''Alumina''' is the chemical <math>Al_2O_3</math>, or aluminium(III) oxide. It occurs naturally as hexagonal crystals called '''corundum''', the second hardest [[mineral]] on Earth.<ref name="Cairncross">B. Cairncross - ''Field guide to rocks and minerals of Southern Africa'' 2004. ISBN 978-1-86872-985-2 pp. 80-82</ref> Used without qualification, '''aluminium oxide''' usually refers to alumina rather than the other oxides of aluminium. Aluminium is the third most common element on Mars after Oxygen and silicon. |
| + | |||
| + | Most aluminium on Mars is not in the form of alumina but rather in the form of alumina-silicates, such as Feldspar. Aluminium is also a component of volcanic rocks such as basalt. | ||
[[File:Alumina.jpg||200px|thumb|rigth|Top: a heap of chemically pure [[Activated_(Chemistry)|activated]] alumina. Bottom left: a sapphire. Bottom right: a ruby.]] | [[File:Alumina.jpg||200px|thumb|rigth|Top: a heap of chemically pure [[Activated_(Chemistry)|activated]] alumina. Bottom left: a sapphire. Bottom right: a ruby.]] | ||
==Characteristics== | ==Characteristics== | ||
| − | The hardness of corundum by definition 9 on Mohs' scale and it has a white streak and vitreous lustre.<ref name=Cairncross />. Corundum has a specific gravity between 3.96<ref name=WebsterJobbins>R. Webster & E.A. Jobbins - ''Gemmologists' compendium'' 7th ed. 2001. ISBN 978-0-7198-0291-1 p. 36.</ref> and 4.1<ref name=Cairncross />. The different varieties have refractive indices varying from between 1.759 and 1.767 to between 1.770 and 1.779.<ref name=WebsterJobbins>R. Webster & E.A. Jobbins - ''Gemmologists' compendium'' 7th ed. 2001. ISBN 978-0-7198-0291-1 p. 36.</ref><br /> | + | The hardness of corundum by definition 9 on Mohs' scale and it has a white streak and vitreous lustre.<ref name="Cairncross" />. Corundum has a specific gravity between 3.96<ref name="WebsterJobbins">R. Webster & E.A. Jobbins - ''Gemmologists' compendium'' 7th ed. 2001. ISBN 978-0-7198-0291-1 p. 36.</ref> and 4.1<ref name="Cairncross" />. The different varieties have refractive indices varying from between 1.759 and 1.767 to between 1.770 and 1.779.<ref name="WebsterJobbins">R. Webster & E.A. Jobbins - ''Gemmologists' compendium'' 7th ed. 2001. ISBN 978-0-7198-0291-1 p. 36.</ref><br /> |
| − | Some corundum, including all rubies, display ''asterism'', which is to say that they reflect light in such a way as to form a six-sided star.<ref name=Cairncross /><ref name=WebsterJobbins /> | + | Some corundum, including all rubies, display ''asterism'', which is to say that they reflect light in such a way as to form a six-sided star.<ref name="Cairncross" /><ref name="WebsterJobbins" /> |
==Variants== | ==Variants== | ||
The colour of a corundum crystal depends on impurities. | The colour of a corundum crystal depends on impurities. | ||
| − | * Red corundum is known as '''ruby'''. | + | |
| − | ::The red color of Ruby comes from an impurity of considerabbly less than 1% Chromic oxide. The chromium is what permits the ruby to be used for a laser, producing red light. <ref>McGRAW-HILL ENCYCLOPEDIA OF Science & Technology 8th Edition (c) 1997, vol 15, page 688.</ref> | + | *Red corundum is known as '''ruby'''. |
| − | * Blue corundum is known as '''sapphire'''. It gets its colour from iron and titanium impurities<ref name=Cairncross /> | + | |
| − | * Colourless (pure) corundum is known as '''white sapphire'''. | + | ::The red color of Ruby comes from an impurity of considerabbly less than 1% Chromic oxide. The chromium is what permits the ruby to be used for a laser, producing red light. <ref>McGRAW-HILL ENCYCLOPEDIA OF Science & Technology 8th Edition (c) 1997, vol 15, page 688.</ref> |
| − | * Other varieties of corundum crystal are known by ''colour'' sapphire. These are pink, yellow, violet and green sapphire<ref name=Cairncross />. | + | |
| + | *Blue corundum is known as '''sapphire'''. It gets its colour from iron and titanium impurities<ref name="Cairncross" /> | ||
| + | *Colourless (pure) corundum is known as '''white sapphire'''. | ||
| + | *Other varieties of corundum crystal are known by ''colour'' sapphire. These are pink, yellow, violet and green sapphire<ref name="Cairncross" />. | ||
==Occurence== | ==Occurence== | ||
| − | On Earth, corundum mainly occurs in [[metamorphic rock]], as well as in [[alluvial deposits]].<ref name=Cairncross /> | + | On Earth, corundum mainly occurs in [[metamorphic rock]], as well as in [[alluvial deposits]].<ref name="Cairncross" /> |
| + | |||
| + | Alumina is commonly found in clays that were created on Mars as a result of gravity and chemical separation in the primordial oceans. | ||
==Use== | ==Use== | ||
| − | * It is used as an [[abrasive]].<ref name=Cairncross /> | + | |
| − | * Used in the production of [[refractory]].<ref name=Cairncross /> | + | *It is used as an [[abrasive]].<ref name="Cairncross" /> |
| − | * Ruby [[laser|lasers]] are based around synthetic ruby crystals, portions of which are doped with [[chromium]]. | + | *Used in the production of [[refractory]].<ref name="Cairncross" /> |
| − | * Alumina | + | *Alumina in clay is an important component of ceramics., bricks and other building materials. |
| − | * Both natural and synthetic corundum is used in jewelry. | + | *Ruby [[laser|lasers]] are based around synthetic ruby crystals, portions of which are doped with [[chromium]]. |
| − | * As a catalyst in the [[Sabatier process]]. | + | *Alumina is the main component of [[aluminium ore]]. |
| + | *Both natural and synthetic corundum is used in jewelry. | ||
| + | *As a catalyst in the [[Sabatier process]]. | ||
==Open issues== | ==Open issues== | ||
| − | * How common are alumina deposits on Mars? | + | |
| + | *How common are alumina deposits on Mars? | ||
| + | *Clay deposits are common. | ||
==References== | ==References== | ||
Revision as of 08:48, 11 April 2019
Alumina is the chemical , or aluminium(III) oxide. It occurs naturally as hexagonal crystals called corundum, the second hardest mineral on Earth.[1] Used without qualification, aluminium oxide usually refers to alumina rather than the other oxides of aluminium. Aluminium is the third most common element on Mars after Oxygen and silicon.
Most aluminium on Mars is not in the form of alumina but rather in the form of alumina-silicates, such as Feldspar. Aluminium is also a component of volcanic rocks such as basalt.
Top: a heap of chemically pure activated alumina. Bottom left: a sapphire. Bottom right: a ruby.
Characteristics
The hardness of corundum by definition 9 on Mohs' scale and it has a white streak and vitreous lustre.[1]. Corundum has a specific gravity between 3.96[2] and 4.1[1]. The different varieties have refractive indices varying from between 1.759 and 1.767 to between 1.770 and 1.779.[2]
Some corundum, including all rubies, display asterism, which is to say that they reflect light in such a way as to form a six-sided star.[1][2]
Variants
The colour of a corundum crystal depends on impurities.
- Red corundum is known as ruby.
- The red color of Ruby comes from an impurity of considerabbly less than 1% Chromic oxide. The chromium is what permits the ruby to be used for a laser, producing red light. [3]
- Blue corundum is known as sapphire. It gets its colour from iron and titanium impurities[1]
- Colourless (pure) corundum is known as white sapphire.
- Other varieties of corundum crystal are known by colour sapphire. These are pink, yellow, violet and green sapphire[1].
Occurence
On Earth, corundum mainly occurs in metamorphic rock, as well as in alluvial deposits.[1]
Alumina is commonly found in clays that were created on Mars as a result of gravity and chemical separation in the primordial oceans.
Use
- It is used as an abrasive.[1]
- Used in the production of refractory.[1]
- Alumina in clay is an important component of ceramics., bricks and other building materials.
- Ruby lasers are based around synthetic ruby crystals, portions of which are doped with chromium.
- Alumina is the main component of aluminium ore.
- Both natural and synthetic corundum is used in jewelry.
- As a catalyst in the Sabatier process.
Open issues
- How common are alumina deposits on Mars?
- Clay deposits are common.
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 B. Cairncross - Field guide to rocks and minerals of Southern Africa 2004. ISBN 978-1-86872-985-2 pp. 80-82
- ↑ 2.0 2.1 2.2 R. Webster & E.A. Jobbins - Gemmologists' compendium 7th ed. 2001. ISBN 978-0-7198-0291-1 p. 36.
- ↑ McGRAW-HILL ENCYCLOPEDIA OF Science & Technology 8th Edition (c) 1997, vol 15, page 688.
