Some interesting technical stuff about diamonds

[kenny]

Diamond is the ultimate gemstone, having few weaknesses and many strengths. It is well known that Diamond is the hardest substance found in nature, but few people realize that Diamond is four times harder than the next hardest natural mineral, corundum (sapphire and ruby). But even as hard as it is, it is not impervious. Diamond has four directions of cleavage, meaning that if it receives a sharp blow in one of these directions it will cleave, or split. A skilled diamond setter and/or jeweler will prevent any of these directions from being in a position to be struck while mounted in a jewelry piece.

As a gemstone, Diamond''s single flaw (perfect cleavage) is far outdistanced by the sum of its positive qualities. It has a broad color range, high refraction, high dispersion or fire, very low reactivity to chemicals, rarity, and of course, extreme hardness and durability. Diamond is the April Birthstone.

In terms of it''s physical properties, diamond is the ultimate mineral in several ways:

Hardness: Diamond is a perfect "10", defining the top of the hardness scale, and by absolute measures four times harder than sapphire (which is #9 on that scale).

Clarity: Diamond is transparent over a larger range of wavelengths (from the ultraviolet into the far infrared) than is any other solid or liquid substance - nothing else even comes close.
Thermal Conductivity: Diamond conducts heat better than anything - five times better than the second best element, Silver!

Melting Point: Diamond has the highest melting point (3820 degrees Kelvin)
Lattice Density: The atoms of Diamond are packed closer together than are the atoms of any other substance
Tensile Strength: Diamond has the highest tensile strength of any material, at 2.8 gigapascals. However, that does not quite translate into the strongest rope or cable, as diamond has cleavage planes which support crack propagation. The strongest ropes can likely be made from another material, carbon nanotubes, as they should not suffer from the effects of cracks and break. Still, if a long, thin, perfect crystal of diamond could be manufactured, it would offer the highest possible pulling strength (in a straight line - don''t try to tie it in a knot!)

Compressive Strength: Diamond was once thought to be the material most resistant to compression (the least compressible). It is the material that scientists use to create the greatest pressures when testing matter. However, the rare metal Osmium has recently been shown to be even less compressible (although it is not as hard as diamond). Diamond has a bulk modulus (reciprocal of compressibility) of 443 GigaPascals (GPa). The bulk modulus of the metal osmium has recently been found to be 476 GPa, about 7% greater than diamond.

Diamond is a polymorph of the element carbon. Graphite is another polymorph. The two share the same chemistry, carbon, but have very different structures and properties. Diamond is hard, Graphite is soft (the "lead" of a pencil). Diamond is an excellent electrical insulator, Graphite is a good conductor of electricity. Diamond is the ultimate abrasive, Graphite is a very good lubricant. Diamond is transparent, Graphite is opaque. Diamond crystallizes in the Isometric system and graphite crystallizes in the hexagonal system. Somewhat of a surprise is that at surface temperatures and pressures, Graphite is the stable form of carbon. In fact, all diamonds at or near the surface of the Earth are currently undergoing a transformation into Graphite. This reaction, fortunately, is extremely slow.

PHYSICAL CHARACTERISTICS:

Color is variable and tends toward pale yellows, browns, grays, and also white, blue, black, reddish, greenish and colorless.
Luster is adamantine to waxy.
Transparency crystals are transparent to translucent in rough crystals.
Crystal System is isometric; 4/m bar 3 2/m
Crystal Habits include isometric forms such as cubes and octahedrons, twinning is also seen.
Hardness is 10
Specific Gravity is 3.5 (above average)
Cleavage is perfect in 4 directions forming octahedrons.
Fracture is conchoidal.
Streak is white.
Associated Minerals are limited to those found in kimberlite rock, an ultramafic igneous rock composed mostly of olivine.
Other Characteristics: refractive index is 2.4 ( very high), dispersion is 0.044, fluorescent.
Notable Occurrences include South Africa and other localities throughout Africa, India, Brazil, Russia, Australia, and Arkansas.
Best Field Indicator is extreme hardness.

Source

 

[kenny]

I was surprised to learn, Cleavage is perfect in 4 directions forming octahedrons.".

I had always thought diamonds had a grain in one direction much like wood.

 

[kenny]

Quote, "Diamond has four directions of cleavage, meaning that if it receives a sharp blow in one of these directions it will cleave, or split. A skilled diamond setter and/or jeweler will prevent any of these directions from being in a position to be struck while mounted in a jewelry piece."

Question:

I have never heard this discussed here.
First of all the setting concern must apply only to rounds since they are the only ones which can be rotated to any orientation over 360 degrees.

How can we know our jeweler set it our round diamond the right position to minimize exposure of the 4 cleavage directions?
Are these cleavage directions identifiable with a polariscope or some other tool?

 

[Garry H (Cut Nut)]

Date: 9/20/2009 3:37:57 PM
Author: kenny
Quote, ''Diamond has four directions of cleavage, meaning that if it receives a sharp blow in one of these directions it will cleave, or split. A skilled diamond setter and/or jeweler will prevent any of these directions from being in a position to be struck while mounted in a jewelry piece.''

Question:

I have never heard this discussed here.
First of all the setting concern must apply only to rounds since they are the only ones which can be rotated to any orientation over 360 degrees.

How can we know our jeweler set it our round diamond the right position to minimize exposure of the 4 cleavage directions?
Are these cleavage directions identifiable with a polariscope or some other tool?

Kenny I have trained my jewellers and setters to look for the thinnest girdle parts and any naturals (very very common) and turn the stones so these are arranged to be at 45 degrees to main axis.
Most rounds are 4 point or cut with the table in the cube plane = 45 degrees to all the octahedral faces. So the clevages are a very real issue - since the girdle will nearly always be thinnest at those points.

The same applies for all squarish stones - and if you have the option for a thicker girdle on 2 sides then set that in the East West orientation since most damage occurrs on those sides -(not the NS ends).

Finally I like to arrange settings the wrong way.
http://www.hollowaydiamonds.com.au/engagement-rings/solitaire/
It does not always work out the way i like because most of my staff prefer the "right way".
but I like the prong next to the shank on a 6 claw setting and I avoid 4 prongs wherever possible after having seen soo many chipped diamonds in them.

 

[Garry H (Cut Nut)]

Date: 9/20/2009 3:12:12 PM
Author:kenny
Diamond is the ultimate gemstone, having few weaknesses and many strengths. It is well known that Diamond is the hardest substance found in nature, but few people realize that Diamond is four times harder than the next hardest natural mineral, corundum (sapphire and ruby). But even as hard as it is, it is not impervious. Diamond has four directions of cleavage, meaning that if it receives a sharp blow in one of these directions it will cleave, or split. A skilled diamond setter and/or jeweler will prevent any of these directions from being in a position to be struck while mounted in a jewelry piece.

As a gemstone, Diamond''s single flaw (perfect cleavage) is far outdistanced by the sum of its positive qualities. It has a broad color range, high refraction, high dispersion or fire, very low reactivity to chemicals, rarity, and of course, extreme hardness and durability. Diamond is the April Birthstone.

In terms of it''s physical properties, diamond is the ultimate mineral in several ways:

1st Hardness: Diamond is a perfect ''10'', defining the top of the hardness scale, and by absolute measures four times harder than sapphire (which is #9 on that scale).

Clarity: Diamond is transparent over a larger range of wavelengths (from the ultraviolet into the far infrared) than is any other solid or liquid substance - nothing else even comes close. 1st
Thermal Conductivity: Diamond conducts heat better than anything - five times better than the second best element, Silver! 1st

1st Melting Point: Diamond has the highest melting point (3820 degrees Kelvin)
Lattice Density: The atoms of Diamond are packed closer together than are the atoms of any other substance
Tensile Strength: Diamond has the highest tensile strength of any material, at 2.8 gigapascals. However, that does not quite translate into the strongest rope or cable, as diamond has cleavage planes which support crack propagation. The strongest ropes can likely be made from another material, carbon nanotubes, as they should not suffer from the effects of cracks and break. Still, if a long, thin, perfect crystal of diamond could be manufactured, it would offer the highest possible pulling strength (in a straight line - don''t try to tie it in a knot!)

Compressive Strength: Diamond was once thought to be the material most resistant to compression (the least compressible). It is the material that scientists use to create the greatest pressures when testing matter. However, the rare metal Osmium has recently been shown to be even less compressible (although it is not as hard as diamond). Diamond has a bulk modulus (reciprocal of compressibility) of 443 GigaPascals (GPa). The bulk modulus of the metal osmium has recently been found to be 476 GPa, about 7% greater than diamond.

Diamond is a polymorph of the element carbon. Graphite is another polymorph. The two share the same chemistry, carbon, but have very different structures and properties. Diamond is hard, Graphite is soft (the ''lead'' of a pencil). Diamond is an excellent electrical insulator, Graphite is a good conductor of electricity. Diamond is the ultimate abrasive, Graphite is a very good lubricant. Diamond is transparent, Graphite is opaque. Diamond crystallizes in the Isometric system and graphite crystallizes in the hexagonal system. Somewhat of a surprise is that at surface temperatures and pressures, Graphite is the stable form of carbon. In fact, all diamonds at or near the surface of the Earth are currently undergoing a transformation into Graphite. This reaction, fortunately, is extremely slow.

PHYSICAL CHARACTERISTICS:

Color is variable and tends toward pale yellows, browns, grays, and also white, blue, black, reddish, greenish and colorless.
Luster is adamantine to waxy.
Transparency crystals are transparent to translucent in rough crystals.
Crystal System is isometric; 4/m bar 3 2/m
Crystal Habits include isometric forms such as cubes and octahedrons, twinning is also seen.
Hardness is 10
Specific Gravity is 3.5 (above average)
Cleavage is perfect in 4 directions forming octahedrons.
Fracture is conchoidal.
Streak is white.
Associated Minerals are limited to those found in kimberlite rock, an ultramafic igneous rock composed mostly of olivine.
Other Characteristics: refractive index is 2.4 ( very high), dispersion is 0.044, fluorescent.
Notable Occurrences include South Africa and other localities throughout Africa, India, Brazil, Russia, Australia, and Arkansas.
Best Field Indicator is extreme hardness.

Source

I stopped after a few 1st''s, but that is what really swung me into being a diamond fan - the amazing thing about diamond is it is amazing

 

[kenny]

Date: 9/20/2009 7:51:00 PM
Author: Garry H (Cut Nut)

Finally I like to arrange settings the wrong way.
It does not always work out the way i like because most of my staff prefer the 'right way'.

but I like the prong next to the shank on a 6 claw setting and I avoid 4 prongs wherever possible after having seen soo many chipped diamonds in them.

Thank you Garry.

Forgive me but this brings up questions.
What is this wrong and right way you speak of?

So apparently a round girdle will have 4 places where it is thinest resulting from polishing against these four cleavage planes.
In a 4-prong setting rotating the diamond so the prongs are at the 4 thinnest girdle points protects the vulnerable cleavage planes from impact?
Do I understand this?

And would not 4 prongs protect a round diamond actually better than 6 because the 4 can be positioned in those 4 most vulnerable points of girdle?

 

[Venice]

kenny, your tech stuff took me back to my Science Olympiad coaching days! I coached rocks and minerals. Thanks!

 

[Garry H (Cut Nut)]

Date: 9/20/2009 10:46:31 PM
Author: kenny

Date: 9/20/2009 7:51:00 PM
Author: Garry H (Cut Nut)

Finally I like to arrange settings the wrong way.
It does not always work out the way i like because most of my staff prefer the ''right way''.

but I like the prong next to the shank on a 6 claw setting and I avoid 4 prongs wherever possible after having seen soo many chipped diamonds in them.

Thank you Garry.

Forgive me but this brings up questions.
What is this wrong and right way you speak of?

So apparently a round girdle will have 4 places where it is thinest resulting from polishing against these four cleavage planes. saw an octahdron in half and round it up with the least loss and you will find you want to stop when the girdle is just thick enough (or only a little too thin) at the 4 narrowest places. These indicate on the finished round stone where the octahedral cleavage zones are and the greatest risk.
I saw a clients stone this morning with a very thin girdle and 2 chips - on opposite sides of the stone. Both had small polished extra facets or maybe naturals under the girdle - which is common because the cutter does this to save the largest diameter and max weight.
I believe that this stone may have sustained one of those chips while it was being held by a 4 prong very high setting. (I can not prove that).
In a 4-prong setting rotating the diamond so the prongs are at the 4 thinnest girdle points protects the vulnerable cleavage planes from impact?
Do I understand this?

And would not 4 prongs protect a round diamond actually better than 6 because the 4 can be positioned in those 4 most vulnerable points of girdle?

 

[4ever]

Thanks Kenny that was very interesting. I''d never though about if a diamond could melt before....

 

[kenny]

Too bad diamond has the highest melting temp, otherwise they could melt the rough and pour the liquid into molds.

100% yield. Zero waste.
Maybe all the gunk that causes inclusions and color would burn away or float to the surface where it could be polished off.
Maybe they'd all be D IF.

It would take gobs of energy to heat to 3820K and would require some engineering.

We just have to find a material that can remain solid at 3820K.

 

[Garry H (Cut Nut)]

Kenny what will you make your molds from?????

 

[kenny]

Yes, therein lies the rub if everything else melts at a temp lower than diamond.

Well, no harm fantasizing.

Hey maybe they could make the molds out of other diamonds that have been somehow treated, zapped, magnetized, electrified, or transmorgified to raise the melting temp, or somehow cooled.

Someone go experiment.
I don't want royalties.
Keep the zillions.
I'm happy.