Alumina: Difference between revisions

Revision as of 19:03, 16 February 2013

Alumina is the chemical $A l_{2} O_{3}$ , 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.

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.
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]

Use

It is used as an abrasive.^[1]
Used in the production of refractory.^[1]
Ruby lasers are based around synthetic ruby crystals, portions of which are doped with chromium.
Alumina can be used as an 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?

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.

[Cairncross-1] 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

[WebsterJobbins-2] 2.0 ^2.1 ^2.2 R. Webster & E.A. Jobbins - Gemmologists' compendium 7th ed. 2001. ISBN 978-0-7198-0291-1 p. 36.

[1]

[2]

@@ Line 1: / Line 1: @@
-{{Stub}}
+'''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>. It occurs naturally as hexagonal crystals called '''corundum''', the second hardest [[mineral]] on Earth.<ref name=Cairncross>''Field guide to rocks and minerals of Southern Africa'' - B. Cairncross. 2004. ISBN 978-1-86872-985-2</ref>
+==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 />
+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 />
-The hardness of corundum by definition 9 on Mohs' scale and it has a white streak, vitreous lustre and specific gravity between 4.0 and 4.1<ref name=Cairncross />. It is used as an abrasive and the production of [[refractory]].
+==Variants==
+The colour of a corundum crystal depends on impurities.
+* 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'''.
+* Other varieties of corundum crystal are known by ''colour'' sapphire. These are pink, yellow, violet and green sapphire<ref name=Cairncross />.
+==Occurence==
+On Earth, corundum mainly occurs in [[metamorphic rock]], as well as in [[alluvial deposits]].<ref name=Cairncross />
+==Use==
+* It is used as an [[abrasive]].<ref name=Cairncross />
+* Used in the production of [[refractory]].<ref name=Cairncross />
+* Ruby [[laser|lasers]] are based around synthetic ruby crystals, portions of which are doped with [[chromium]].
+* Alumina can be used as an [[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?
 ==References==