Spinel vs. Ruby:
The Thrilla (not) In Manilla

by Rusty Shackleford

http://www.emporia.edu/earthsci/amber/go336/webpages.htm

Table of Contents

  • Introduction
  • Mineral Properties
  • History
  • Gems and Pricing
  • Mark McGwire
  • References

    •

    Introduction

    For centuries spinel and ruby have been a source of conflict, pitting brother against brother, nation against nation, Aber against Aber, oops... I mean and neighbor against neighbor. Okay, so maybe the conflict is not that serious. Maybe there is not even a controversy, but these two gems do have a storied past together and today are directly connected. Spinel and ruby share many similarities and as a result they have been repeatedly mistaken for one another. Spinel can be considered the pyrite of ruby or the Fool's Ruby, if you will, seeing as how spinel is usually cheaper to buy than ruby. Spinel is also known as the great imposter (citation). Unlike pyrite and gold though, spinel and ruby are not as easily distinguished. You will not see anyone biting down on ruby, because with hardness over eight they would be as toothless as gold prospectors. This webpage will tell of the history and similarities of the two and you can judge for yourself if ruby really deserves to be considered the alpha gem.

    Spinel image (left) taken from www.jewelryexpert.com/
    CATALOG/graphics/197-Radiant-Red-Spinel.gif    .
    Ruby image(right) taken from www.gemfix.com/images/
    stones/ruby/ruby108.jpg    .

    I needed a webpage project in a mineralogy course and chose this topic originally as a joke. In the arcade game Resident Evil 4, you find Spinel as you go and you can sell it to make money,. So the joke was that I would use facts about spinel based entirely on the game. It would have been something like this...
    Spinel is found primarily in a rural, remote village in Spain. It is commonly found in barrels, on cultists, and being carried by crows. All pieces of spinel look exactly like all the rest and each of them is worth exactly 2,000 Pta.
    Of course, that might have been more unacceptable than the webpage I ended up with, which is a difficult thing to accomplish.


    Yea!



    Here's one suspiciously left on the roof. And...



    Although small in size, they appear to have some value.
    Photo taken by Sa... I mean Rusty Shackleford.

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    Mineral Properties

    Spinel and ruby belong to the mineral-chemical classification group of oxides, but spinel is a magnesium-aluminum oxide and the other, an aluminium oxide. So they are similar in many ways, but some physical properties cause them to get mixed up and I thought I would start with those. The first one that stands out is the red color they both exhibit, although spinel is normally a little more on the pink side. Incidently, the red color in both is caused by the same agent, chromium.
    Spinel can be found in other colors such as green, blue, or black but let us just pretend it is not so (wink wink). They both have a vitreous luster, and this glassy look can be seen in the pictures on this page. The most noticeable difference between the two is in the crystal system and shape. Spinel is an isometric gem that usually forms octohedral crystals whereas ruby is rhombohedral and forms hexagonal prisms.
    They can also be differentiated by their optical properties. Ruby is dichroic and spinel displays no pleochroism, which means that ruby splits the light sort of like a prism and spinel does not. Ruby is doubly refractive and spinel is singly refractive, which means when light enters ruby it is split and travels slower but at two different speeds and in spinel, light is only slowed and moves on out of the stone.
    It is not surprising that they are as similar as they are. The formation of both minerals is interlocked together. One example of this is how they are found in Sri Lanka together in the same areas on this island. These minerals are found in metamorphic rock and the type of environment they form in has high temperatures. The chemical composition of both spinel and ruby contain aluminum and oxygen. Spinel forms when those two elements combine with magnesium, but once all the magnesium is locked up in spinel, then rubies begin to form. That is how they are found in the same place and also why people thought they were the same mineral.

    Spinel


    Image taken from
    http://www.addmorecolortoyourlife.com/img/01-gemstones/gemstones/spinel.jpg


    Basic Information
    Property Spinel Ruby
    Chemical Makeup MgAl2O4 Al2O3
    Chemical Class Spinel Oxide Corundum Oxide
    Crystal System Isometric Rhombohedral
    Hardness 8 9
    Specific Gravity 3.7 4
    Luster Vitreous Vitreous
    Cleavage None None
    Fracture Conchoidal to uneven Conchoidal to uneven

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    The Black Prince's Ruby in the Imperial State Crown. Image taken from www.palagems.com/
    Images/ball_spinel_article/black_princes_ruby.jpg

    History

    The name for spinel comes from the Greek word spina which means "thorns" and refers to the sharp edges of it in a natural form. Ruby is much simpler, it comes froms the word ruber which means "red". They both have been used for many centuries, but only until recently has it been shown that they are two different minerals. Many of the oldest and most famous rubies are actually spinels. Rulers such as Henry VIII of England, and Peter the Great of Russia, thought they had amazing rubies when actually they had was spinel. The most famous example is the Black Prince's Ruby that is one of the English Imperial Crown Jewels. It first came into British possession in the 14th century in exchange for the protection of a Spanish ruler named Don Pedro. Perhaps the terms would have been different if they had known it was not an actual ruby. Today this spinel is set in the cross pattée of the State Crown and can be viewed below and in the Tower of London. I would bet it is as valuable as ruby given its current status with the Brits. Another famous gem, The Timur Ruby, is a 352 carat spinel that has been owned by many emperors and has always been thought to be a ruby.


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    Gems and Pricing

    So it has been established (hopefully) that spinel and ruby are similar. Both gems are commonly faceted and used in jewelry. Why then, is the pricing so different for each of them? Ruby is usually considered about ten times as valuable as spinel (citation?).
    For a more solid example, I found one site that would sell a one carat spinel for around $900, and the same site sold a one carat ruby for around $4,000 (citation?). The highest price per carat ever paid for a ruby was last year when an eight carat ruby that had been faceted went for 2.2 million dollars (citation?).
    When speculating about the reason for the price difference, the first thought that comes to mind is that ruby is harder to find than spinel. This is not the case, actually, spinel has become much more difficult to find but that fact has barely affected the price of it. There may actually be a lot more of them out there, but they are all being called ruby. One of the factors affecting the price is the difference in hardness. Ruby is 9 on Mohs Hardness Scale, but spinel is 8, which makes it one of the hardest minerals out there. I do not think that would be enough to constitute that big of a price change.


    Spinel
    Image taken from
    www.jewelryexpert.com/
    CATALOG/graphics/
    Red-Spinel-Ring-
    III-13a.gif
    Ruby
    Image taken from
    migo.sixbit.org/papers/
    Introduction_to_Ruby/ruby-
    diamond-ring-8.gif


    Ah, he'll buy it at a high price.
    Image taken from
    www.armchairempire.com/images/Reviews/gamecube/
    resident-evil-4/resident-evil-4-1.jpg         		Another small difference that plays a part in the price difference is color. Ruby is usually found in a darker shade of red. Spinel is normally cleaner or free of inclusions and so more clear than ruby, but at the same time can also have impurities or fractures, which keeps it from having a distinct advantage in this area. Another advantage that ruby has is that it is commonly enhanced through heating and other processes while spinel is not, but I would consider this like using steroids. Ruby is the Mark McGwire of gems. So physically they do not have huge differences that account for such a large difference in price, in my opinion. I think it comes down to the fact that rubies have a "name" to go with the face, whereas Spinel is largely unknown. This can keep rubies in larger demand than the equally beautiful spinel.


    I sure can see the resemblance.
    Images taken from     www.noulakaz.net/weblog/images/
    20060606-ruby.jpg     (left!) and home.ripway.com/
    2004-4/95613/Blogs/Media%20Images/McGwire.jpg     (right!)


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    Conclusion

    I think it has been shown that spinel and ruby are physically, nearly identical, and their prices should reflect that but do not. I think spinel is getting gemmed by the whole situation. I believe it comes down to the fact that Ruby has a certain mystical or legendary sense about it. When people hear ruby, they think about something like great kings or Arabian Nights. When people hear spinel they may think you are talking about a laundry detergent or computer programming language. I think if you took that part away from the rubies, then they would be equal to spinel in many ways including price. Perhaps if they switched places, and ruby was just recently discovered, maybe it would be the less expensive of the two, even with the same physical properties. Finally, I would not hesitate to buy a spinel as a gift for someone and claim it as a ruby, and if they are good enough to tell the difference then they have earned the right to slap me.


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    References

    ...and for Related Links
    Emporia State University
    www.emporia.edu     		Gemology Webpage on Ruby
    www.emporia.edu/earthsci/amber/
    go340/students/hess/index.htm
    GO 340 Student Webpage Projects
    www.emporia.edu/earthsci/amber/
    go340/students/stupages.htm         		GO 336 Student Webpage Projects
    www.emporia.edu/earthsci/
    amber/go336/webpages.htm

    For more information email saber@emporia.edu or ssomerha@emporia.edu.
    Return to the mineralogy, www.emporia.edu/earthsci/amber/go336 or student webpages, www.emporia.edu/earthsci/amber/go336/webpages.htm.

    2006 No copyright on text... steal, steal, steal! The big S himself, Rusty Shackleford.