Do you remember blacklights when we were kids? Well we're going to use them to go rock hunting! Here in San Benito County one of the most common yet unusual rocks we find is fluorescent Calcite.
In a rock shop you'll find Calcite in many forms such as tumbled stones, crystals, and mixtures such as septarian marble. When you rock hound for calcite in San Benito County, you usually find calcite mixed with other stones. As a rock forms and changes over time there are often holes, cracks, or air pockets created in the stone. Over time water seeps into these cavities and crystals grow. When the water contains dissolved calcium carbonate, the crystals formed are calcite. You can find calcite mixed with all kinds of other minerals in the same rock. The fun part of calcite is that it often glows under a blacklight (blacklights release ultraviolet, UV, energy which is not seen by your eye). The colors seen under the blacklight include bright pink, bright orange, and light green. All you need to see the fluorescent colors is a black light. To go out rock collecting use a black light flashlight (you can pick one up at TOPS Rock Shop). Its easy to find Calcite in the San Benito River bed, in local creek beds, or along a rocky hillside. You'll be amazed at the beautiful colors you will see in the dark with your blacklight. You can also stop by TOPS and check out the UV / Blacklight room! There are several types of fluorescent rocks on display. Calcite can be clear or translucent. Clear meaning you can see through the stone and translucent meaning you can see light through the stone.
Calcite can be found in many different areas of the world and as part of many different stones. For example, the crystals in Septarian Marble are yellow calcite. For those who want to know a little more of the science of Calcite, Calcite is a mineral which is composed of calcium, oxygen and carbon, CaCO3. Calcite is soft, with a Mohs hardness of 3.0 on a scale of 10. Calcite has a crystal form that is called a trigonal-rhombohedral, see the diagram above from http://www.nps.gov/history/history/online_books/jeca/thompson/sec3.htm. Calcite comes in many colors including green, golden, orange, blue, clear, red and pink. Small or trace amounts of iron, magnesium, chromium, phosphorus, and other elements give calcite its color and fluorescent qualities. The color you see under the blacklight will usually be different that the color you see with your eyes in normal light. Rock Happy!