Hexagonal Prisms in Amethyst Crystals

Amethyst is a purple form of quartz. I became fascinated with the structure of the crystals after zooming in on this photograph of an amethyst geode that I took a week ago in New Hampshire at Gemstar Gemstones in Enfield. I saw the individual crystals in the photos below. This was the first time I ever saw a hexagonal prism in "real life." I have read that the crystals have a tetrahedral structure. Tetrahedrals are one of the five Platonic Solids (regular polyhedra). I also read that amethyst crystals are trigonal, meaning they have three-fold symmetry. An excellent discussion of trigonal crystals appears here.

To see more amethyst crystals, click here.

Here, I zoomed in on the first photo. You can see the six-sided prisms here.

If you have Apple's QuickTime software click here to see an interactive QTVR crystal of amethyst. Click here to view an interactive 3D model of the amethyst structure (this will open a new browser window).

Here I zoomed in even further and clearly saw the hexagonal prism.

If only we had the time to teach polyhedra to our students in the field while we collect rocks. I know they would never forget the experience or the mathematics.

Gemstar Gemstones Set

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ABC Wednesday: J is for Jasper

John and I went to Gemstone Gems and I learned about jasper for the first time:

Jasper is an opaque,[1] impure variety of silica, usually red, yellow or brown in color. This mineral breaks with a smooth surface, and is used for ornamentation or as a gemstone. It can be highly polished and is used for vases, seals, and at one time for snuff boxes. When the colors are in stripes or bands, it is called striped or banded jasper. Jaspilite is a banded iron formation rock that often has distinctive bands of jasper. Jasper is basically chert which owes its red color to iron(III) inclusions. The specific gravity of jasper is typically 2.5 to 2.9.[2]

Jasper. (2009, March 5). In Wikipedia, The Free Encyclopedia. Retrieved 00:23, March 22, 2009, from en.wikipedia.org/w/index.php?title=Jasper&oldid=27512...

A wall of jasper beads of all different colors.
Gemstar Gems Set

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Cats Tuesday: Cat's Eye Cats

John took me to see Gemstar Gems in Enfield, New Hampshire this weekend. We found these tiny cats made from cat's eye. Cat's eye is a quartz with the quality of chatoyancy — a fancy name for a fancy gemstone.

Better known as a cat's eye this stone is named for the actions of a cat's eye when exposed to light. The line forms an aperture that opens and closes as it is rotated under a direct light source.

For more information, see Your Gemologist here.

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