DIAMONDS AND DIAMOND SIMULANTS

Diamonds have been used in jewelery, especially in engagement rings for over six centuries.

REMARKABLE 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. They are carried to the surface in diamond pipes,as inclusions in a rather ordinary looking rock known as kimberlite.
more information on kimberlites
To ensure they are not converted to graphite,diamonds must be transported 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.
They are found in many localites, both overseas and in the US.

This movie (68 k) shows that diamonds do not form in the kimberlite magma but are carried up to the surface by the magma.

Diamond is made of carbon (C). The stable form at the Earth's surface is graphite.
Diamond is the hardest material (except, maybe lonsdaleite, the hexagonal polymorph of diamond); graphite is the softest !! See MOHS harness scale

HOW DO WE KNOW THESE THINGS ?

Age: from Carbon dating ???
NO!!...... C-dating only works for very young carbon. You need to use U-Pb or other radioactive decay schemes to date inclusions in diamonds. Inclusions are around 100 microns in diameter (0.1 mm).
NOTE: Kimberlite magmas carry diamonds to the surface. The kimberlites (kimberlite pipes) are often much younger.
Under what conditions do diamonds form?
- geothermometry: temperatures of 900 - 1300 C
- geobarometery: pressures of 45 - 60 kB
  - Note: 30 kB = 100 km = 60 miles
  - 50 kB = 150 km = 90 miles
  - 60 kB = 200 km = 120 miles
Where is C from ? May be from near-surface carbonates or from deep mantle.

MINING:

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 % are sold in a 'managed selling environment') and the remainder are used for industrial purposes: 'bort' or 'carbonado' (carbonado is finer).

Where are diamonds found?: some brief history of diamond mining

Additional material on mining and resource aspects of diamonds.

CHARACTERISTICS OF DIAMOND:

Hardness = 10
Crystal System = cubic
Other
Natural crystal form: octahedral - these are uncut crystals
- diamonds also come in cubic as well as octahedral form
- has four cleavages, thus tends to break on impact.
- e.g., stream beds: diamonds

Famous diamonds

Dresden
Hope ...the real thing!
Cullinan (Before)
- After
Sancy
Tiffany
Kohinor
- a-section
Shah
Nassau
Florentine
The Great Mogul
Orloff
Stern
Regent

VALUE

The 4 "C" words:
1. COLOR
2. CLARITY
3. CUT
4. CARAT WEIGHT
  Some further comments on the '4 C's from another source!

(1) COLOR: done by 'grading' visual comparison with 'knowns' or by instrumental means.

consider the amount of yellow color:
blueish-white -> white -> silver -> yellow
'Fancy' colors have their own appeal:
yellow and greens,browns and greens, as well as shades of pink ( larger pink diamonds are quite rare and currently very expensive)

(2) CLARITY : presence of blemishes or flaws, scratches, nicks, 'naturals' (the original surface of an uncut stone). There are many systems of nomenclature.

Some terms include:

flawless or perfect
imperfect
very slightly imperfect
very very slightly imperfect

F1  VVS1  VVS2  VVS3  VS1   VS2  SI1   SI2    I1   I2   I3
flawless					            imperfect

"first pique" inclusions readily recognizable at 10x mag., not significantly diminishing brilliance
"second pique" larger inclusions, can be seen with naked eye
"third pique" many large inclusions, diminishing brilliance

Examples:

(3) CUT

Facets are placed so as to maximize the brilliance and fire of a stone.

Remember that in the first lecture we talked about how the proportions of a faceted gemstone are determined based on the refractive index.

A poorly cut stone is characterized by poor proportions and misplaced facets, etc.

Recall the basic concepts:

Refraction is dependent upon the wavelength
RI is proportional to wavelength; red RI < violet RI
Dispersion is due to the different amounts different wavelength are bent
Fire,which is seen as rainbows and glints of c olor, is a consequence of the cut of the stone:
- due the prism effect.
  Review the light path in a correctly cut gem!
  Brilliant Cut (American cut)
VERY GOOD ... GOOD .... MEDIUM ... POOR
There are many alternative diamond cuts. For example, "Tolkowsky flower cuts", which were introducted in the 1980s.
(4) CARAT WEIGHT
Recall: 1 carat = 0.2 g, thus 5 carats=1g
This site explains the GIA grading report used for diamonds, including information on desirable characteristics
Canadian approximate price lists
Some very useful information and "straight talk" from Peter Mylnek

Other issues: Treatment, simulants, synthetics

(1) TREATMENTS:
- (c) irradiation and heating
  
  (a) 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 inclusions: use of a laser. Hair-wide diameter hole through which solutions can be infiltrated to bleach colored inclusions.
  
  (c) Irradiation and heating: RESULT: changes the color of the diamond. A common color produced by irradiation is green.
  Look for: color zoning that follows the shape of the cut of the gem and not original crystal features (e.g., cleavages)
  Early attempts: beginning of 20th Century: diamonds exposed to radium
  PROBLEM: they remained radioactive !
  
  Modern irradiation and heat treatment: stones do not remain radioactive
  PROBLEM: difficult to detect treatment
  
  (1) linear accelerators
  (2) gamma ray facilities
  (3) nuclear reactors *
  
  Electron irradiation: PRODUCES COLOR CONCENTRATION AT THE CULET or KEEL LINE
  If irradiated from the side:
  examine at low angle: see "body color"
  examine by viewing down onto table: see apparent color
  
  If irradiated from below
  From below gives color concentration around crown facets.
  
  Natural blue diamonds contain the element boron, and this changes the conductivity of the diamonds.

(2) SIMULANTS

Simulants - simulate the appearance of diamond, but ARE NEITHER MAN-MADE OR NATURAL DIAMOND!

You could go crazy staring at all the different colors of diamonds:

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

YAG

GGG

CZ
Strontium titanate
diamond

(YAG= yttrium aluminum garnet; GGG = gadolinium gallium garnet; CZ= cubic zirconia.)

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

Various properties

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

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

(3) SYNTHESIS (Details on gem synthesis)

Synthetic diamonds are often yellowish in color (supposedly these are not released for gem purposes, but used as diamond grit for industrial purposes).

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