OK, it has been a few minutes since I posted any pictures of rocks, so brace yourselves.
I figured out how to get a picture of a rock with the UV flashlight. The camera won't pick up the light so I had to do it during the daytime and illuminate the rocks from behind. Take notes, there may be a test.
Today's experiment is with chalcedony. (Kal-se-dunny). It is a cryptocrystalline quartz but is more of a
category than an actual mineral. Agate, jasper, onyx, carnelian, etc. are all forms of chalcedony. Chalcedony is a mixture of quartz and moganite. Both are silicate minerals but have different crystal structures. Moganite is often green-colored due to the presence of nickel.
Typically, chalcedony is found in rounded shapes or nodules. But not far from Rapid City is a place where it formed in sheets and looks like gray frosted glass. The various minerals in it are what give it its colors because the minerals reflect different frequencies of light.
This is how they look in indirect sunlight.
But under a fluorescent light, like the one above my kitchen sink, other tints are visible.
In between the layers of the stone are tiny pockets of quartz crystals. You can see the black grit from the rock polishing has gotten into the pockets.
Some of these pockets are very deep, which makes cleaning the grit out of them quite difficult even using a Waterpik.
Here are some comparisons showing lighting effects.
Incandescent light vs fluorescent light
The nickel in the Moganite reacts by fluorescing green under short-wave ultraviolet light.
The quartz component reacts blue under long-wave UV (black light). Same stone.
That concludes today's mineralogy lesson. I lied about the test.
