Archives of Ask A Scientist!

About "Ask A Scientist!"

On September 17th, 1998 the Ithaca Journal ran its first "Ask A Scientist!" article in which Professor Neil Ashcroft , who was then the director of CCMR, answered the question "What is Jupiter made of?" Since then, we have received over 1,000 questions from students and adults from all over the world. Select questions are answered weekly and published in the Ithaca Journal and on our web site. "Ask A Scientist!" reaches more than 21,000 Central New York residents through the Ithaca Journal and countless others around the world throught the "Ask a Scientist!" web site.

Across disciplines and across the state, from Nobel Prize winning scientist David Lee to notable science education advocate Bill Nye, researchers and scientists have been called on to respond to these questions. For more than seven years, kids - and a few adults - have been submitting their queries to find out the answer to life's everyday questions.

Previous Week's Question Published: 20 December, 2006 Next Week's Question
Real ruby is considerably harder, more dense than 'fake' gemstone
Question
How can you tell if a ruby is real or fake? Is there a test I can do?

Question
Ruby, the gemstone, is the red variety of the mineral corundum. Corundum is crystalline aluminum oxide (alumina). Ruby's red color comes from a small amount (a percent or so) of chromium impurity that substitutes for aluminum in the crystal structure. Other impurities give corundum other colors: gem sapphire occurs in a blue variety where the impurities are iron and titanium Naturally occurring ruby crystals formed slowly at high temperature deep in the earth. A rock containing ruby is unmistakably "natural" as the rock texture is not reproducible in the lab. Also diagnostic are small mineral inclusions in natural ruby.

"Fake" ruby results from mis-identification of another red mineral, commonly garnet or tourmaline, or of colored silica glass. These mis-identifications are relatively easy to detect making use of physical properties. For instance, ruby is much harder than tourmaline, garnet, or especially glass. As well, fake rubies are often less dense than the real thing. It's easy to do these physical tests.

Now comes the hard part: telling natural from synthetic ruby As is the case for diamond, a lot of ruby crystals have been grown (synthesized) in the lab. Growing rubies is by no means easy, but unlike mis-identified ruby, synthetic ruby is no less "real" than natural ruby. It can be extraordinarily difficult to tell the two apart. In the Verneuil synthesis process (used for over a century), rubies are grown by dripping fused alumina onto a plate, where it crystallizes. Characteristically curved growth features--observed with a microscope-- remain in the synthetic single crystal and are tell-tale signs of a synthetic origin. Heat treatment changes the internal features of the crystal making detection of this type of synthetic ruby more difficult. More recently, the appearance and physical properties of ruby crystals grown in a flux can be made to be essentially identical to those of natural ruby. Chemical analysis to detect trace amounts of impurities characteristic of the flux--like lead-- may be the only way to tell natural from synthetic.

Interested is seeing some natural ruby and corundum? Come to the Snee Hall mineral museum on the Cornell campus!