RUBIES BY ACCIDENT IN THE OCCIDENT Presented March 7, 2007 by Andre Mongeon

Note: Some material has been added. Links are provided to the pictures originally used to avoid re-publication of copyrighted images.

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RUBY

-A red variety of Corundum (Al2O3)

-All other colours of gem corundum are "sapphire"

-Rubies are coloured by a small amount of Chromium and an even smaller amount of Vanadium that substitute for the Aluminum. These trace elements usually make minerals green. The variety of beryl (Emerald) is an example where either chromium or vanadium causes the colour of the mineral to be green.

-Rubies are relatively rare

-Generally, the higher the chromium content, the more they fluoresce under black light (LW).

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Notable Occurrences-

Myanmar (Burma), Afghanistan, Pakistan, Vietnam Thailand, India, Sri Lanka, Tanzania, Madagascar, Greenland, Russia, Norway

Although corundum occurs in pegmatites, most Rubies are found in Metamorphic rocks

-Marbles

-Schists

or in alluvial deposits derived from them. Corundum is much harder than the host rock.

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Creation of Rubies in the Afghanistan-Vietnam Marble belt

In the past (over 75 million years ago), much of India was situated beside what is now East Africa.

 

Plate tectonics-

Large pieces (plates) of the earth’s surface are moving very slowly in various directions. Those that move away from each other are called divergent. Those that move toward each other are convergent.

 

<= = D I V E R G E N T = =>

===> CONVERGENT <===

 

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INDIA

SEDIMENTARY, MY DEAR WATSON...

As India approached Asia, the ocean gave way to a sea (Tethys Sea). The sea lasted long enough for significant sedimentary rock (limestone) to build on the sea floor.

The plates continued to converge until the sea disappeared. Much like an "accident in very slow motion".

Then the Himalayan mountain range began to form.

See wikipedia article/map: http://en.wikipedia.org/wiki/India_Plate

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A WORK IN PROGRESS

India is still converging with Asia. As a result, the Himalayas continue to rise.

This convergence is also the cause of many earthquakes in the area when the plates "slip". Where plates collide, there is an increased chance of volcanic activity in the area.

BONUS-

This convergence has also brought some deeply buried rocks close to the surface. Many mineral "goodies" that would normally be too deep to mine are found here, like the Topaz of Pakistan.

 

See the topaz gallery at mindat: www.mindat.org\gallery.php?min=3996

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METAMORPHIC MOMENTS. Change is good...

The limestone was subjected to great pressure and some of it was pushed below the surface where it eventually melted, cooled and formed marble. The marble was later pushed back near the surface by the convergence.

An intermittent "band" of marble can be found in a crescent shape area that approximates the collision area of the Indian and Asian plates. Essentially, this "band" extends from Afghanistan through Pakistan, Nepal, Myanmar, Thailand and Vietnam.

 

See the map of Asia at wikipedia: http://en.wikipedia.org/wiki/Asia

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SO WE HAVE MARBLE, SO WHAT?

Aluminum, Oxygen and small amounts of chromium and vanadium are needed to form rubies. Marble is a Calcium/Magnesium carbonate, which does not seem to bear any chemical relationship to ruby. Rubies are made in not made from marble

But there is more...

UNWANTED

The presence of iron (and titanium) will change the colour of corundum, depending on the levels, to orange, blue or other colours. The presence of silica tends to cause other minerals to form instead of corundum.

The puzzle is how iron and silica (very common) were absent and the aluminum and chromium (rarer) were in the marble.

When or after the marble was formed, the iron and silica were somehow melted or leached away, leaving a fairly pure marble.

 

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ENTER THE DRAGON, ---IGNEOUS PROXIMUS

Some have suggested that a granitic intrusion can accomplish the purification of the marble. What little Iron that was left tended to form pyrite, which is sometimes found near the rubies.

The majority of the Iron and its compounds present may have also sank before the marble cooled.

Perhaps minerals made of these elements had formed crystals in the marble. The vacated minerals may have left voids in the marble where rubies could grow hydrothermally. In this process, the elements needed to make ruby would have been dissolved in very hot water or steam under great pressure. When the solution cools to just the right temperature, rubies can "freeze" as they turn from a gas or liquid to a solid.

JUST A DASH OF SALT

All that was needed was aluminum and oxygen with a dash of chromium and a pinch of vanadium. The metals are thought to have been provided by various salts that could have been concentrated from the sea sediments.

 

IMITATION, THE SINCEREST FORM OF FLATTERY

There are two main ways in which synthetic rubies are made. One involves flowing a hot vapor of chemicals over a seed crystal (the Verneuil process). The other is the "Flux" process where a mix of chemicals is melted to a liquid state and slowly cooled until rubies crystallize. Both use high heat, cooling and solidification, largely copying natural processes.

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RUBY RECIPE

Aluminum, Oxygen, Chromium and Vanadium.

Mix well and bake at 670 degrees C and allow to cool to 620 degrees C for a long time and voila. Rubies.

Just like good cookies, there are never enough to satisfy the demand.

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RUBIES ARE RED, SAPPHIRES ARE BLUE

The Chemical Elements, Geological Forces and Temperatures required to create Rubies have to be just right. Aluminum, Oxygen and Chromium and a dash of Vanadium in the right quantities, not too little or too much pressure and heat.

Plus the absence of very common elements.

Plus slow, even cooling over long periods.

Plus the deposit has to be close enough to the surface to be found.

When all these combine you see that

RUBIES ARE RARE AND BEAUTIFUL TOO...

 

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FACETED STONES

 

See ebay for pictures of faceted stones

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Desired qualities in cut stones.

Rubies are pleochroic- often appearing pink/purple-red in one direction and orange-red at the other. Good rubies are cut using the pink/purple colour axis.

The best colour is often referred to as "pigeon blood" which is a bright red, fluorescent in daylight. In actuality, fresh pigeon blood is very bright electric pinkish-red when observed during Asian rituals.

Zoned (unevenly coloured) stones are cut with the best colour at the bottom. Glass or garnet topped doublets use a piece of good ruby at the bottom and it dominates the colour of the stone.

Small amounts of rutile (titanium oxide) give a "silk" effect. Larger levels in hexagonal patterns give rise to star-rubies. The colour is usually less red as some of the titanium replaces the aluminum.

Clarity is important to value. Flawless, eye clean stones are very expensive, therefore some flaws are usually tolerated-

*Inclusions of other minerals, gases or liquids

*Zoning, an uneven colouring

*Minor Cracks

*A certain amount of cloudiness (not opaque if possible)

*Less than perfect colour

 

These flaws are not all bad. Synthetic Ruby is cheap and near perfect. Flaws can serve to authenticate genuine ruby.

Rubies are often heat treated to improve the colour and reduce the cloudiness. Iron and Titanium oxides are "damaged" LEAVING behind the red colour only---like leaves in autumn...

 

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Collecting Ruby Crystals

Try to obtain undamaged and terminated crystals if possible

Size Matters - Bigger is more expensive

Colour- Do you collect many shades or seek a few choice ones?

3 general shapes, all 6 sided- "pencil" section, sharply tapered or hexagonal disc like (tabular).

If collecting matrix specimens look for ones with accessory minerals if possible - "Collectors combo".

Locations- Some locations are more affordable- India (in schist), or Pakistan (in marble) for example.

 

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Not quite Turkish Delight, but candy all the same.

 

For pictures of Ruby crystals, see mindat.org: www.mindat.org/gallery.php?min=3473

 

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REFERENCES

Indian Plate, Asia, Plate tectonics: .http://en.wikipedia.org

Pictures from www.mindat.org

Ruby data, locations: www.mindat.org/min-3473.html

Sasso, A. The Geology of Rubies www.discover.com/issues/nov-04/departments/geology-of-rubies/

deWind, A. Rubies in the Dust www.geolsoc.org.uk/template.cfm?name=RubiesInTheDust

Gemstone Forecaster, part one www.mindat.org/gallery.php?min=3473