Facts About DIamonds

Diamond facts

* All diamonds are at least 990,000,000 years old. Many are 3,200,000,000 years old (3.2 billion years)

* Diamonds are formed deep within the Earth: between 100 km and 200 km below the surface.

Diamonds form under remarkable conditions!

o The temperatures are about 900 - 1300 C in the part of the Earth's mantle where diamonds form
o The pressure is between 45 - 60 kilobars (kB)
+ 50 kB = 150 km = 90 miles below the surface
+ 60 kB = 200 km = 120 miles below the surface
Diamonds are carried to the surface by volcanic eruptions.

The volcanic magma conduit is known as a kimberlite pipe or diamond pipe. We find diamonds as inclusions in the (rather ordinary looking) volcanic rock known as kimberlite.

NOTE: The kimberlite magmas that carry diamonds to the surface are often much younger than the diamonds they transport (the kimberlite magma simply acts as a conveyer belt!).

* Diamond is made of carbon (C), yet the stable form (polymorph) of carbon at the Earth's surface is graphite.

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* To ensure they are not converted to graphite, diamonds must be transported extremely rapidly to the Earth's surface.

It is probable that kimberlite lavas carrying diamonds erupt at between 10 and 30 km/hour (Eggler, 1989). Within the last few kilometers, the eruption velocity probably increases to several hundred km/hr (supersonic!).

* Diamond is the hardest material

Diamond is the hardest gem on MOHS harness scale and graphite (also made from carbon atoms) is the softest !! Given that both diamond and graphite are made of carbon, this may seem surprising.



The explanation is found in the fact that in diamond the carbon atoms are linked together into a three-dimensional network whereas in graphite, the carbon atoms are linked into sheets with very little to hold the sheets together (thus the sheets slide past each other easily, making a very soft material).

Diamonds occur in two general types of deposits world wide:

* volcanic pipes, also known as kimberlite pipes
* alluvial, or placer, deposits, which were formed by the erosion of diamond pipes over millions of years.

The earliest productive mines were in the Golconda region of India, particularly along the Kristna River. After 1725 this mining district was gradually eclipsed in importance by the diamond deposits of Brazil. Diamonds were first mined there along the Jequitinhonha River, in the Diamantina area of the state of Minas Gerais.

In 1867 a 21-carat stone was discovered on the banks of the Orange River near Hopetown, South Africa. A great diamond rush started, and new deposits were discovered that were more productive than any the world had ever known. Another major diamond resource was developed in the 1950s in the Yakutia region of the Soviet Union. By the 1980s the Yakutia and South African regions and the country of Zaire dominated the world's diamond market. The mineral has also been found in smaller amounts in numerous other places. In the United States the leading producers include Arizona, Nevada, and Montana, although the largest gemstones have been found in an eroded volcanic pipe in Pike County, Ark.
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For many years, microscopic diamonds have occasionally been noted in meteorites; they were attributed to high-speed collisions in space or with the Earth. In 1987, however, following the discovery of many more such diamonds, the theory was developed that they are the product of ancient supernova explosions of giant stars.

In recent years, diamonds have been found in unusual metamorphic rocks that were subjected to very high temperatures and pressures.


HOW RARE ARE DIAMONDS?

· How many grams do you need to mine to get 5 grams of diamonds?

(5g/1000 kg) @ 1000 g/kg = 5 g /1,000,000 g!

BUT only 20 % are gem quality (80 % of these are sold in a 'managed selling environment') and the remainder are used for industrial purposes (this material is known as 'bort' or 'carbonado' (carbonado is finer)).


CHARACTERISTICS OF DIAMOND:

· Hardness = 10

· Crystal System = cubic

· This is what crystals look like before they are faceted: note their natural octahedral shape!

Uncut diamonds are also found in cubic forms

· Diamond has four good cleavages, thus diamonds tend to cleave on impact

· Other diagnostic properties.


Other issues: Treatment, simulants, synthetics

(1) TREATMENTS:

* (a) filling of cracks

Surface cracks and cleavages reaching the surface: often with a glass-like material

Identification: optical microscope examination:

+ =greasy appearance
+ =flash effect
+ =bubbles

Problem: Filling does not always resist polishing and cleaning

* (b) drilling of inclusions
+ Drilling inclusions involves use of a laser.

Solutions can be poured into the resulting "hair-width" diameter hole to bleach colored inclusions.

* (c) irradiation

Irradiation is used to change the color of the diamond. A common color produced by irradiation is green.

Early attempts: beginning of 20th Century: diamonds exposed to radium - the problem was that the diamonds remained radioactive!! However, modern irradiation treatments do not produce radioactive stones.

Irradiation involves the use of devices such as:

o (1) linear accelerators

o (2) gamma ray facilities

o (3) nuclear reactors

Detection of irradiation treatment:

Electron irradiation only changes the surface of the stone. Thus, it produces a concentration of color where the gemstone is thin. For example, electron irradiation produces a color concentration at the culet or keel line of the faceted gem

(2) SIMULANTS

Simulants - simulate the appearance of diamond

The distinction between a synthetic diamond (man-made diamond consisting of carbon atoms arranged in the typical diamond structure) and a diamond simulant (not a carbon compound with the diamond structure) is VERY important!!

In order of increasing R.I., the most common simulants are:

1. YAG = yttrium aluminum garnet
2. GGG = gadolinium gallium garnet
3. CZ = cubic zirconia
4. Strontium titanate
5. diamond.

This rhyme can be used to memorize the common diamond simulants in the above order:

You go crazy staring at diamonds.

Again: Simulants (look alsikes) differ from synthetics (synthesized by humans!) !!!!

Simulants are distinguished from diamonds using measurement or observation of various properties, such as:

o R.I.
o "Read through effect"
o Dispersion
o Hardness
o Specific Gravity
o Reflection pattern
o Shadow patterns

Note: not all diamond simulants have been around for the same length of time!

(3) SYNTHESIS (Details on gem synthesis)

Synthetic diamonds are often yellowish in color (rarely used for gem purposes, more commonly used as diamond grit for industrial purposes. Modern synthesis of thin film diamond has other industrial applications).

A 5 mm diamond (0.5 carat) takes over a week to grow. Synthesis requires:

* high pressure
* high temperature
* a special apparatus

Synthetic diamonds can sometimes be distinguished from natural diamonds by the presence of flux inclusions (Ni, Al or Fe).

Also see Other Blog on Diamond: Diamonds Exotica