Corundum is a crystalline form of aluminum oxide that occurs naturally in various colors depending on impurity levels. It is the second hardest mineral after diamond. Synthetic corundum is produced from bauxite and is of high quality and cost competitive with natural sources. Rubies and sapphires, gemstone forms of corundum, are rarely mined from host rocks and are instead concentrated in stream deposits through weathering. Corundum is used for both its hardness as an abrasive and when clear, as a gemstone.

1. Corundum

2. • Corundum is a crystalline form of aluminum
oxide (Al2O3) with traces of iron, titanium and
chromium.
• It is one of the naturally clear transparent
materials, but can have different colors when
impurities are present.

3. Cr+ =
Fe & Ti+ =

5. • The name "corundum" is derived from
the Tamil word kuruntam meaning "ruby“
• Corundum is a very hard, tough, and stable
mineral. It is the hardest mineral after
Diamond

6. Properties
Member of : Hematite Group
Crystal System: Hexagonal
Hardness: 9
Cleavage: None

7. Properties
Toughness: Excellent
Specific Gravity: 4.00 (3.99-4.02)
Transparency : Transparent, Translucent, Opaque
Colour: Colourless, blue, red, pink, yellow, grey,
golden-brown

8. Synthetic Corundum
• Corundum was the first gem mineral to be
synthesized in the lab by a process known
today as flame fusion ; producing synthetic
corundum from bauxite.
• The synthetic corundum is of high quality and
cost-competitive with corundum from natural
sources.

10. Applications
For Natural Corundum
• Ruby and Sapphire are the most famous
gemstones after Diamond for jewelries
• It is commonly used as an abrasive on
everything from sandpaper to large machines
used in machining metals.

11. Applications
For Synthetic Corundum
• Industrial applications today include use as
"jewel" bearings in instruments and fine watches.
• For windows in optical scanning devices
• Abrasive etc.

12. Mining Rubies and Sapphires
• They are rarely mined from the rocks in which
they form. Instead, they are usually mined from
stream sediments.
• Rubies and sapphires are very hard and resistant
to chemical weathering

13. Mining Rubies and Sapphires
• Their high specific gravity, relative to other
sediment particles, often causes currents to
concentrate them in small deposits.
• Most rubies and sapphires are produced by
washing the gravels of these stream deposits.

15. Geographical distribution1
Economics2

16. Known deposits of corundum in this
country are sufficient to supply only a
small fraction of the requirements of
American industries.
Between $3,000,000 and $5,000,000
worth of corundum has been produced in
Montana. Before mining was discontinued
in 1929, the Yogo deposit yielded
sapphires, chiefly gem material, value'd
at about
$2,500,000 in the rough.
Geographical distribution1 Economics2

17. This
price was presumably for 90
percent corundum and compares
with
prices from ~69 to ~107 for similar
grades from Africa in
1941-43.
From 1881 to 1895 inclusive,
the market price of domestic
corundum, as summarized in
Bureau of Mines Information
Circular
7295, ranged generally from
$150 to $200 per short ton.
Economics2Geographical distribution1

18. 4 corundum axes dating back to
2500 B.C.E from the Liang Zhou
culture have been discovered in
China.
Emery grade corundum is found
on the Greek island
of Naxos and near Peekskill,
New York, USA. Abrasive
corundum is synthetically
manufactured from bauxite.
Corundum for abrasives is
mined in Zimbabwe, Russia, Sri
Lanka and India. Historically it
was mined from deposits
associated with dunites in
North Carolina, USA and from
a nepheline
syenite in Craigmont, Ontario.
Geographical distribution1

19. With a melting point at 2010°,
corundum makes for a great
material to withstand high
temperatures. Commonly used
in the lab, corundum crucibles
can stay stable for long periods
of time at 1600°.
Sometimes the mineral is even
carved into different shapes for
specialized jobs, such as
triangular shapes for the
manufacture of knives.
USES:
When corundum is found
opaque, its' physical properties
serves great industrial uses.
With a hardness of 9 on Moh's
scale, corundum grains of
various sizes are used as an
abrasive.
Economics2

20. Economics2