Crystal Lab

Uncut Diamond from Western Australia.  Diamond has isometric symmetry with an octahedral crystal habit.  When light passes from the air into water, glass, crystals or any other transparent or translucent substance, the light bends.  This is called Refraction.  Diamond has a much higher refraction than glass, and most other materials.  The power of breaking up white light into its constituent colors is called Dispersion. In this, diamond is likewise very marked.  The blue rays of light undergo a much greater refraction when passing into diamond than do the red rays; hence the spectrum produced by a prism of diamond is very wide - the red and blue ends being widely separated.  This results in the beautiful play of brilliant, prismatic colors upon which so much of the beauty of diamond depends, and which differentiates it so markedly from other colorless stones, such as quartz, topaz, and colorless sapphire, which have lower dispersion.

Aquamarine on Calcite from Pakistan. Aquamarine is a transparent, blue variety of beryl.  Beryl has hexagonal symmetry. In all minerals with symmetry other than isometric, the velocity of light will be faster in certain directions of the crystal than others.  This is called anisotropic , and it can create interesting optical effects.

Questions that Crystal Lab will be Designed to Help Explore:

1. In science class, most of us have used a triangular prism of glass to produce a spectrum.  Is this the shape that produces the clearest, brightest, widest spectrum?  If not, then what shape does?
2. Is the prism shape that produces the widest spectrum dependent on the type of light source?   In other words, does one shape produce the widest spectrum in sun light, and a different shape produce the widest spectrum in incandescent light?
3. Diamond has higher refraction and higher dispersion than glass.   However, a diamond cut into a triangular prism of the same size and shape as a glass triangular prism gives less "fire" or prismatic effects than does the glass.  Why?
4. A common and simple test that jewelers use to distinguish cut, unset diamonds from imitations is to place the flat top of the stone on a dark surface. When looking straight down on the pointed side of the stone (called the culasse), you will not be able to see the dark surface through a diamond.  If the stone is made of glass, then you will see a large, dark center surrounded by a narrow, bright ring.  Can this test be used to distinguish Diamond from Spinal, Rutile, Cubic Zirconia, or Yttrium Aluminum Garnet?   By the way, Diamond is the hardest known substance, however, all good imitation diamonds will scratch glass. If the scratch test is applied to something  hard enough to differentiate an imitation from a diamond, then you could ruin a beautiful, and expensive imitation.
5. Yttrium Aluminum Garnet has about half the dispersion as a Diamond, and Cubic Zirconia has one and a half times more dispersion as a Diamond.  At what angles should each of these imitations be cut so as to best mimic the "fire" of a diamond?  Are the differences in cut large enough to notice by a trained, but unaided eye?
6. Emeralds are usually cut in style called a "step cut".  On the culasse (lower portion) of step-cut stones, there are usually from 4 to 5 series of facets.  Each of these facets are of the same width, and in passing from the girdle to the table they become successively less and less steeply inclined.   What optical property of an emerald does this most accentuate?  Why?  Why are diamonds rarely cut in this way?
7. If you place a calcite crystal on a printed page and view the printing through the calcite, you will see a double image of each letter.  Why?
8. Calcite is not usually made into jewelry because it is very soft (hardness of 3 on Moh's scale).  If you were to cut calcite, what shape would most accentuate its optical properties?
9. Why does a rainbow have the shape of an arc?
10. Why can pure reds be found only in the vertical portions of rainbows?  Fraser points out that this simple feature of pure reds being restricted to the vertical portions of the rainbow somehow escaped notice until his paper of 1972.  Even the most commonplace features of the outside world still afford fresh understandings and surprises.
11. Why is the color sequence in the secondary rainbow opposite that in the primary rainbow?
12. Why is the secondary rainbow seldom seen?
13. Why can only two rainbows be seen in the sky?  If the primary rainbow is due to a single reflection of light rays inside the raindrops, and the secondary rainbow is due to a double reflection, should not there be more rainbows resulting from further  internal reflections?
14. Why is the region of sky between the primary and secondary rainbows darker than the rest of the sky?
15. If you place a coin in a transparent, open jar filled with water and look down through the water surface from the appropriate angle, you see the coin's image on the surface of the water.  Putting your hand on the far side of the jar usually has no effect on the image, but if your hand is wet, the image will disappear.  Why?
16. In a forest, during a partial solar eclipse, all of the little patches of light on the forest floor form crescent moon shapes.  They are actually focused images of the partially eclipsed sun.  How does this happen?

Future Work:

1. Crystal Lab should be able to display crystals in three dimensions, and allow the user to create and manipulate crystals in three dimensions.
2. Crystal Lab should allow the user to view crystals in a verity of light source.
3. Users should be able to move the light source close to or far from the crystal, and should be able to scroll through the space between the light source and the crystal.
4. There should be simulated black cards that can be placed in various locations to create pinholes, pencils of light, etc.
5. Users should be able to choose from many more types of crystals.
6. Users should be able to create and luminate more than one crystal at a time.
7. Crystal Lab should be able to display areas of water drops, and allow the user to specify, size, and density.  Also the user should be able to zoom in on individual water drops and view the internal reflections and refractions.