Diamond
Characteristics
- Habit - octahedrons and cubes with rounded edges and slightly convex faces
- Form - cubic
- Hardness - 10
- Cleavage - perfect octahedral
- Fracture - conchoidal
- Streak - will scratch streak plate
- Lustre - adamantine
- Colour - colourless, yellow, pink, red, green, blue, brown, black
Introduction
Most commercially important gem in the world. Hardest known substance (Mohs' 10). Not indestructible as when struck in right direction can be broken and cleaved. High lustre and high dispersion (bending of white light into colours). When cut & polished attain great beauty with characteristics of brightness, scintillation and fire.
Most common as the colourless but has a range of colours - yellow/pink/red/green/blue = 'fancy coloured' diamonds.
Lore: ward off evil; Greek 'adamas' means invincible so name refers to hardness.
Formation
Composed of pure or near pure carbon. Mill to bill years old, forming at great depths where there is increased temp and pressure.
Some pure and rare diamonds are often very heavy.
Diamonds get to the surface by volcanic eruption (in rare volcanic rocks called lamproite or kimberlite). Eruption forms pipe-like bodies that are mined. These pipes can be eroded by weathering. sediments are carried away from the pipes and contain diamonds which will be incorporated into sand and gravel = alluvial deposits.
Can be transported to the ocean, coastline or sea floor.
World's largest earth moving operation is on the coast of Namibia. Moving sands on old beach gravel to reveal the diamonds beneath, eroded from their source in South Africa, mills of years ago.
Large diamond found = the Cullinan. 3106 carats, found 26th Jan 1905 in Premier Mine, South Africa. Cut into 9 major stones (screen cut out at this point).
History
Used in jewellery since antinquity, first uncut, then after 1300s as cut stones. Many centuries only source was alluvial, in India.
The discovered in Brazil in 17th cent., also alluvial. exploration from these finds led to diamonds found on dry land - first diamond pipes. Since then have explored oldest rocks of a continent in Russia, Canada, Australia.
Today most diamond gem production comes from Botswana, Russia, Canada and South Africa. 80% diamonds not suitable for jewellery and are used industrially. Of those that are gem quality only 1 in 1000 are estimated to have fancy colour and once discarded, now fetch high price.
4 Cs
Once cut are judged on clarity, size, cut and colour (mostly the lack of).
4Cs:
- 1) colour - graded on relative whiteness or rarity of fancy colour
- 2) clarity - freedom from inclusions
- 3) cut - style & quality
- 4) carat weight
Colour & clarity are judged in comparison with defined guidelines. Diamonds are colour graded D (colourless) to Z (light yellow).
Convension when describing colour modified by another is to state the obvious colour last eg: bluish-green = green stone with elements of blue. Stones with two colours of equal intensity say 'red-purple'. To complete the description a colour grade is added as a prefix to indicate saturation (light, fancy, intense, vivid) and tone (deep, dark). Fancy stones are described eg: 'fancy deep pink'.
Grades and observation are documented in diamond grading reports that accompany each stone. Naturally coloured diamonds have a gem'l report confirming authenticity of the colour and fetch high prices.
Fancy
Grading is same as colourless in terms of clarity and cut but depth of colour has its own pricing scale.
Pink/blue/green is rarer than yellow. On GIA grading scale Z stones are more yellow or brown. To receive a fancy label, must be darker in tone or saturation than Z & have noticeable face-up colour. Stones that show a hint of any colour when viewed face up are termed fancy.
Pink Star: As of 2020 record auction for any gemstone; 59.60 carat; fancy, vivid pink diamond; US $71.2 mill in 2017.
Oppenheimer Blue: fancy, vivid, blue; sold for US $57.5 mill in 2016; then the most exp. sold per carat at $3.93 mill.
Aurora Green - fancy, vivid, green; sold for US $16.8 mill in 2016.
Lab Diamonds & Treatments
Synthetic known as laboratory-grown or laboratory-created. Known since 1950s but only recently been produced cost-effectively in gem quality and production quantities in order of mill. of carats.
Detecting syn diamonds, in large or small carats, as loose stones or set in jewellery is an industry concern. Now gem'l knowledge and se of instruments results in quick ID of natural stones in most cases.
Luminescence patterns can reveal growth typical of syn.
Treatments: Most common is to modify colour or clarity. Includes irradiation with or without subsequent annealing; laser treatment; HPHT (high pressure high temp); surface coating; fracture filling. All treatments should be disclosed down the supply chain and on diamond reports.
Arab Roots of Gemolgy
Some elements from 'Arab roots of gemolgy: Ahmad ibn Yusuf Al Tifaschi's Best Thoughts on the Best of Stones' (c.1240) trans. Samar Najm Abul Huda. The Scarecrow Press, London, 1998.
Pliny said diamond is a gold base stone, nothing can spoil it except lead. It started initially to be gold but drought and the presence of salt prevented this.
It is found with ruby, as pebbles in the ruby mines, transported by wind and rain from their host rock. Found in a valley in India, scatterd n the bed , ranging in size from the mustard seed to barley grain. Tender meat pieces are thrown into the valley where eagles see them, rub the earth with them and the diamonds adhere to the meat.The eagles carry it away and the diamonds fall off. Perisan gem dealers having visited China and India, say there is a diamond of magnificant brilliance which can be projected onto a wall, piece of cloth or person's face, by producing light of various coloured rays, similar to a rainbow. It is worn by dignataries. The rest of diamonds that do not show this dispersion are used for cutting corundum and given to merchants.
Two varieties:
- zayti - most valuable, white mixed with a tinge of yellow, similar to colour of oil and resembling pharonic glass
- billawri - strong white colour similar to rock crystal
Characteristics - all varieties have fixed angles, surrounded by surfaces of triangular shape. if it breaks, it breaks in triangular shapes. It can cut every stone while it itself is extremely difficult to break. Can be broken if placed in a tube of lead and carefully hit by some hard instrument. It attracts flies and if the piece is amll enough the fly swallows it. If a person swallows even a tiny piece it tears their intestines and kills them on the spot. Then a group of jewllers from the Maghred andthe Mashreq told me they had swallowed small pieces without being harmed...stone free of snakes' saliva either because of their initial location or some other reason do not cause any above mentioned harm. Another characteristic, mentioned by Aristo, is the great affinity between diamond and gold that it sticks to gold wherever it is. Diamond is cold and hard in the fourth degree.
If a person suffers from a stone in the bladder and urinary tract - a piece of diamond stuck firmly with mastic on a probe made of copper or silver can be intoduced as a catheter and the diamond will shatter the stone. Useful against strong stomach pains if hung extenally over the abdomen. If worn by a newborn at birth it can protect from fear and epilepsy. Can polish, whiten and clean teeth but if retained in the mouth could kill if it retained on it some of the snake's venom, as it is found in the valley of the snakes.
