Monday, May 6, 2013

Recognizing Ruby and Sapphire in Nature

Several rubies in a schist from the Wind River Mountains, Wyoming. Most prospectors would misidentify these as rubies,
but if you look close, you will see distinct, parallel cleavage in one of the rubies - something that does not occur in garnet.

Best of Show - Rubies, sapphires, and iolite gemstones found in Wyoming and faceted in Sri Lanka.
When you think of ruby and sapphire, you probably think of spectacular, faceted, over-priced gems in rings and necklaces. Unfortunately, Mother Nature does not facet her gems: so the gem prospector must learn to recognize the natural, physical characteristics of this gemstone to identify the raw material in the field. The prospector must also learn where to look in the field.

I remember receiving a 25-year pin from the State of Wyoming for my service in finding several hundred $million in gemstones, gold and diamonds for the State. It was a tiny plastic pin about the size of nickel that had a tiny red ruby. After examining this valuable ruby with a microscope, it was obvious it was a synthetic ruby almost too small to weigh. The ruby was likely worth about $1.00 and and the pin another $1.00. Have no idea where it was made, but I would guess China. Why thank you Wyoming for thinking about me.

When it comes to learning how to identify minerals, there are serious flaws with most gemstone books - they are not designed for the prospector. Essentially all show spectacular faceted gems or museum quality specimens that you are unlikely to find in nature. I'm too poor to afford cut gems, so I have to find my own in the rock. So, here are some hints of where to look and what to look for.

The two photos above show the characteristic outline of corundum (the geologists term for ruby and sapphire). The upper photo is a cross-section of ruby in schist showing the characteristic hexagonal (6-sided) cross-section and the lower photo shows another corundum (pink sapphire) at an angle perpendicular to the upper photo. The mineral is still hexagonal, but now we are viewing the long axis which shows what geologists call a prism.

One of the few minerals that you might mistaken for ruby or sapphire is garnet. But don't feel bad as I've known geologists who make this mistake.

Ruby and sapphire also have atomic flaws known as parting where we can see these atomic planes in the crystals and these surfaces also provide locations for twinning of crystals. This are actual planes in the mineral that many gemologists use to break the mineral, or avoid when they cut the mineral. These are useful in identifying the mineral because they do not occur in garnet. But few people are familiar with the term 'parting', so for our purpose, we will refer to these parting planes as "Cleavage", and corundum (sapphire and ruby) have three directions of parting ('cleavage').

Here is a very nice sapphire I found in Wyoming, but the gem cutter did a very poor job of avoiding flaws. For a
 geological researcher, this is a very nice specimen as it can be used to show cleavage and show others how one should not
 cut a gemstone. This cleavage is a plane of weakness and should have been avoided. The mineral should also have not
 been cut showing the dark mineral inclusions and it needed to be polished.

Another pink sapphire that I found that shows excellent rhombohedral cleavage in the gem. Note the two intersecting
 planes that are nearly perpendicular to one another.

Beautiful pink sapphire from Wyoming. The stone is flawed with numerous intersecting cleavage (parting) planes that can
 be partially hidden by cutting the stone in a cabochon.

This was likely the largest ruby ever found on earth! And it was found in Wyoming!  It exhibits excellent color but you are
 probably wondering what I'm talking about because you likely only see green zoisite with a little bit of ruby color. When
 this ruby formed, this entire specimen was one, very large, ruby. But it became unstable at deep in the earth's crust and
 reacted with metamorphic fluids until much of the ruby was replaced by the zoisite. Imagine wearing a ruby this size in a
 necklace. The base of the ruby was cut by a diamond-bladed rock saw.  Even though this ruby was flawed, it provides us
 with a general idea of what might be found in this particular deposit at depth. If this is ever mined, one likely will recover
some very large rubies hidden beneath the surface.
Some corundum, such as this Oriental Amethyst (its not amethyst
but jewellers use this term for violet colored sapphires) will
produce twinned crystals attached to one another.

Here is a beautiful ruby that unfortunately is flawed with rhombohedral
cleavage. Even so, it makes a great gemstone. It is very rare to find a ruby
that is not flawed. Most are translucent like this one. I found this ruby south of
Encampment Wyoming.

Would you recognize these as rubies?  These rubies were found by my son Eric Hausel and they show nodular texture.
This photo shows a pink to violet sapphire prism to the left and a purple-red (pigeon's blood red) ruby in the rock to the
 right. The ruby is surrounded by what is known as a reaction rim of green zoisite.
In this photo, I'm holding rubies recovered from the Granite Mountains of Wyoming. Again, note that the rubies are
 enclosed by a reaction rim of green zoisite. This suggests that these rubies were all part of one large ruby at one time and
 part of the gem reacted with metamorphic fluids to produce the zoisite.
Another twinned Oriental Amethyst - you should be able to see that this corundum has two crystal that grew side by side.
Large, faceted red ruby from the Palmer Canyon ruby-sapphire-kyanite-iolite deposit in the Laramie Mountains. Note the
 distinct parallel cleavage planes.
Look closely at this pretty little gem sapphire from Montana. It is pitted with
rounded edges unlike a sapphire found in outcrop or in eluvium. This is because
it is a placer sapphire that was transported some distance downstream for the source
beds. Several years ago, I found some of the nicest sapphires and benitoite in a
stream in California. None were pitted which suggested that they originated from a
nearby serpentinite.
See anything interesting in this rock? Well it contains about 15 to 20% sapphire. All those light gray to light blue equigranular crystals are sapphire. Many of Wyoming's mountain ranges were subjected to favorable high pressures and temperatures in the geological past for ruby and sapphire. In places where there was sufficient aluminum and little silica, lots of rubies and sapphires crystallized. I suspect that Wyoming has many dozens of ruby and sapphire deposits that remain undiscovered.
Sapphire schist from Palmer Canyon, Wyoming. Note the abundant white to very light blue hexagonal mineral grains. These are all sapphire and this particular sample has about 10% sapphire.

Some of these gemstones will provide few hints of what they are. This 12-carat pink sapphire has an irregular shape, and is nearly flawless, But if you look closely, you will find at least one very distinct cleavage plane and also hints of rhombohedral cleavage.

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