Recognizing Ruby and Sapphire in Nature

Low-quality corundum (variety - ruby) in a schist from the Wind River Mountains, Wyoming
(found by Dr. Ron Frost). Many prospectors would misidentify these as garnet, but look close, and
you will see distinct, parallel cleavage in the largest ruby - 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 gems: so a gem prospector must learn to recognize the natural, physical, characteristics of this gem to identify raw material in the field. And a prospector also needs to learn where to look in the field, and how to identify possible host rocks.

Some time ago, I received a 25-year longevity pin from the State of Wyoming for my service to the State. It was a tiny, plastic pin about the size of nickel that had a tiny, red, ruby. So, I took this spectacular gem to my lab to examine with a binocular microscope, and it was obvious that it was a synthetic ruby almost too tiny to weigh. The ruby may be worth about $1.00 and and the pin another $1.00 (pre-Biden prices). No idea where it was made, but my guess is China. If the state government had any creativity, one would think they would search for a good, Wyoming rock hound to dig some  Wyoming rubies (and other gems), facet them, and make them into longevity and dedication pins for their employees. As such, Wyoming would actually contribute to the state's economy and also provide a great means of advertising for the state's natural resources. Employees would be proud, particularly after they learned a little information about the history and gemology of the gems! 

When it comes to learning to identify minerals, there are flaws with most gemstone and mineralogy books - they are not designed for prospectors or rock hounds. Essentially, all books show spectacular, faceted, gems or museum-quality mineral specimens that are rare. 

Corundum in schist cut perpendicular to prism, showing 
distinct outline of hexagonal crystal habit. Sample from Wind
River Mountains collected by Dr. Ron Frost. Locality could
not be verified.

Hexagonal, prismatic corundum (pink sapphire) in vermiculite
schist, collected from Palmer Canyon, Wyoming. Yellow arrows
point to numerous crystals of pink corundum.

The two photos above show the characteristic crystal habit of corundum (geologists' term for ruby and sapphire). The upper photo shows a cross-section of ruby in schist with a characteristic hexagonal (6-sided) crystal habit, while the lower photo shows another corundum (pink sapphire) with its crystal habit perpendicular to crystal in the upper photo. This lower mineral is still hexagonal, but now we are viewing the long, crystal axis, which shows what geologists call a prism (or prismatic crystal habit). One mineral that is sometimes mistaken for ruby or sapphire, is garnet. But don't feel bad as I've known geologists who make that same mistake.

Ruby and sapphire exhibit atomic flaws known as crystal parting: linear, structural (atomic) planes in a crystal. This are actual planes in a mineral that gemologists might to break a mineral, or avoid when cutting the mineral, because they are a zone of weakness in the crystal. These are useful in identifying minerals like corundum (ruby, sapphire) and they do not appear in garnet. Few people are familiar with the term 'parting', but it is similar to mineral "cleavage". Corundum (sapphire and ruby) typically exhibits three directions of parting.

Pink sapphire from Palmer Canyon, Wyoming showing distinct plane cutting through the edge of
the gem. This is what is known as a parting plane. Most mineralogists describe corundum as having
three parting planes, while a few report the presence of at least one cleavage. However, cleavage
appears to be absent in corundum.

A 12-carat ruby collected in Palmer Canyon, Wyoming held by tweezer. Note the parallel lines
(twin planes) in the side of the crystal.

Beautiful pink sapphire from Wyoming. The stone is flawed by numerous intersecting (parting
planes.

Possibly, the largest ruby on earth (prior to alteration to the green zoisite! Yes, this was once all
 ruby, prior to changing physical conditions in the geological past that resulted in much of the
 former ruby being replaced by another mineral.  When the ruby formed, the entire specimen was
one, very-large, ruby. But it became unstable at depth in the earth's crust and reacted with
metamorphic fluids until much of the ruby was replaced by more stable zoisite. Imagine wearing a
ruby this size in necklace. The base of the ruby was cut by a diamond-bladed rock saw.  Even
 though the ruby was flawed, it provides us with a example of what may lie deeper at depth. 

This Oriental Amethyst (its not amethyst
but jewellers use this term for violet-colored
sapphires) will produce twinned crystals attached
to one another.

A beautiful ruby flawed with rhombohedral
parting. Even so, it makes a great gemstone. 
Most are translucent like this one recovered south of
Encampment Wyoming.

 These rubies were found by my son Eric Hausel and show nodular texture.

Pink to violet sapphire prism (left) with a purple-red (pigeon's blood red) ruby in rock
  (right). The ruby is enclosed by green zoisite reaction rim.

Ruby from Granite Mountains, Wyoming. Note the rubies are enclosed by green zoisite reaction rim. 
The zoisite reaction rim and ruby form a porphyroblast within the host rock - fuchsite schist.

Twinned Oriental Amethyst (oriental amethyst is an archaic term for lavender-colored corundum.

 

Pitted gem sapphire from Montana with rounded crystal faces.
This sapphire was collected from placer and the rounded crystal
faces are due to erosion and stream transportation.

Serpentinite with 15 to 20%, light-blue,  equigranular, sapphire discovered in the Granite Mountains
Wyoming by Robert Odell.

Sapphire schist from Palmer Canyon. 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.