calcite - fluorescent calcite cleavage rhombs from Mexico - Unit of 5 student specimens
$ 12.50
Calcite, CaCO3, is an extremely common rock forming mineral. In pegmatites it forms large masses and it makes up some limestones almost entirely. It has a large variety of crystal forms, but these do not include the rhombus-shaped pieces that are sold as “calcite crystals.” The rhombs are produced by cleaving calcite in three directions between rows of atoms.
When calcite is free of impurities and is optically clear, it exhibits double refraction. When it is placed above a line drawn on paper and rotated, the drawn line doubles and becomes single depending on the angle of rotation. These are excellent examples of cleavage rhombs and are a decent size for your students, though not clear enough to show double refraction.
Under longwave ultraviolet, many of these specimens fluoresce hot pink. Under shortwave, some specimens exhibit a pale blue fluorescence and also a phosphorescence that is fairly slow to extinguish. In a phosphorescent substance, electrons that absorb energy slowly re-emit it, sometimes glowing for minutes or even hours as they return to their original energy states. Most phosphorescent compounds are fast emitters, however, with lifetimes on the order of milliseconds. You can watch this calcite extinguish as the atoms return to their normal energy state after exciting it with shortwave for a few seconds.
These clean sharp rhombs of variously-colored calcite are from the Challenger Cave system near Monterrey, Nuevo Leon, Mexico, a famous locality for fluorescent calcite.
Most ultraviolet flashlights are inexpensive and all are longwave. These will give you the hot pink fluorescence. To excite this calcite to see phosphorescence, you will need strong and well-filtered shortwave lamp. We can recommend The Triple, sold by Way Too Cool, LLC at https://www.fluorescents.com/products-the-triple.html. It will give short, medium and longwave ultraviolet.
The photos are representative of what we ship. Click photo once to select, again to enlarge.
With each set of five we add two smaller specimens. If you would like calcite chips to use to demonstrate that calcite effervesces with hydrochloric acid releasing carbon dioxide, let us know and we'll add a bag of smaller rhombs to your order, no charge.
Making multiple purchases? Click on the "combine shipping" button in the shopping cart. We'll send an invoice with combined shipping. It may not be instantaneous, since a human has to take a look and we might be out in the field during the day. A link in that invoice will bring you back to checkout, no hassle.
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