Calcite is the most common of the fluorescent minerals, giving off a wide range of colors under ultraviolet light.

I am a student at Grosse Pointe South high school and I completed this research as an independent study during my senior year.

My goal was to develop a procedure for easily quantifying the spectra of calcite to determine if the ions involved could be identified. Since much is unknown about the chemical nature of fluorescence in minerals, it was an opportunity to try to develop techniques for understanding their nature.

Variations in the fluorescence of calcite are due to changes in the spectral frequency, which may be attributed to the presence of different trace ions in the mineral. The goal of this research was to determine which ions may be involved and how their performance changes with variations in environment.

Nuevo Leon Calcite from Nuevo Leon, New Mexico

White Light, Shortwave UV Light, and Longwave UV Light, Respectively.

I began by gathering calcite from many different locations and recording characteristics for each specimen. All of these locations were researched in an attempt to gather information about their chemistry. Upon examining the visible characteristics of each sample, attributes like zoning and double refraction were found. All of the samples were divided into non-destructive and destructive categories, depending on the owner's wishes. A work area was created to develop a technique for taking fluorescent pictures of calcite samples and their spectra. My first attempt was made using a digital camera and placing a diffraction grating over the lens of the camera in an attempt to get the spectra. However, there was insufficient visual light given off by most of the samples for the camera to operate. I then found success in using a Quickcam and a precision spectroscope.

I quickly discovered that several background materials interfered in getting the correct spectra including the wall, my hand, the surface on which the mineral was placed, and the reflection of the UV lamp off the calcite. Black construction paper was found to be non-fluorescent and was used to cover all surfaces in the work area. Non-fluorescing modeling clay was used to keep the minerals in place while taking their spectra. In addition to getting spectra, pictures of the minerals were taken in long wave and short wave ultraviolet light. I used a series of felt covered boxes to hold the UV lamp in position over the mineral sample while I took its picture. The camera was unable to process the image in the correct color so imaging filters were used to change the image to the visible color.

Set-up of minerals during heating and cooling process.

After these steps were completed, I began the process of breaking the destructive samples into three groups of hot, cold, and room temperature for heating, cooling, and comparison. One set of the samples was heated for 20 min at 475 F in an oven and one set of the samples was cooled to 78.5 C for 20 min by packing them in dry ice. These temperatures were chosen because it was the largest extreme of environment that could be reached with the materials available. This time interval was used to allow the entire sample to reach its surrounding temperature. Each heated and cooled sample was then compared to its room temperature variant under both short wave and long wave ultraviolet light. Pictures of the images that were noticeably different from their counterpart were taken and their spectrum was obtained. I waited for the altered pieces to return to room temperature and again checked them under both short wave and long wave UV light.

To calibrate the spectroscope, a helium gas discharge tube spectrum image was made with the Quickcam. By looking up the major emission lines in helium and matching them up to the spectroscope's scale, I was able to calibrate the spectrum in Angstroms by matching the principle line of Helium (5870) to the spectroscope scale. I didn’t know at the time that the spectroscope scale was not linear. This resulted in an error in the wavelengths on my graphs, one that gets worse with distance from the calibration line. Future research should take this into account. Black construction paper was used to prevent any interference in the quality of each specimen's spectra. Non-fluorescent modeling clay was used to hold the minerals in place while their spectrum was made. When short wave ultraviolet light was used, I wore special ultraviolet safety goggles and latex safety gloves to prevent any penetration of short wave UV light to my skin.

I gathered 57 pieces of calcite in total, of which 30 were fluorescent. These samples were from many widespread locations such as Atikokan, Ontario, Chihuahua, Mexico, Morocco, Franklin, NJ and the Johnny Bull Mine, NM. I also obtained 12 pieces with unknown origin. A data book was assembled containing ultraviolet photographs of the minerals in both wavelengths, white light photographs, spectra of the minerals taken under ultraviolet light in both wavelengths, and graphs of the quantified spectra. Also included are data tables containing information on each mineral including origin, type, known chemistry, colors, special effects, and certain associated minerals, and specific filters used in each mineral's ultraviolet photograph.

In order to analyze my data, a number of computer programs were used. Digital images and spectra were taken in white light, short wave UV, and long wave UV, and Adobe PhotoShop was used to enhance the images to the right color and quality. The spectra from the Quickcam were converted into grayscale, and transferred to a different format so they could be opened in NIH Image. Once changed, each spectra was quantified in angstroms and analyzed to find their peaks and their starting and end points. The NIH file images were converted into intensity plot profiles for use in Microsoft Excel format and spreadsheets of each mineral were set up. PSI Plot was used to create the spectra graphs. Patterns and trends were found in the graphs of the spectra and each graph was placed into three categories based upon the range of their emission wavelengths: Broadband spectra (B) (3000 Angstroms), Medium band spectra (M) (2000 Angstroms), and Narrow band spectra (N) (1000 Angstroms). The graphs were also sorted by the wavelength of the peak of their continuum curve. They were divided into three general categories based on their peak emission wavelength and fluorescent color.

Franklin, NJ Calcite. Shortwave and Longwave Spectra Respectively.

Profile graphs were developed by combining all of the minerals that contained the same known chemistry, such as samples containing manganese, organics, or rare earth elements. I then compared unknowns to them to see if their chemistry could be determined. The profile method appeared to be successful. I was able to identify the chemistry of ten unknown samples by matching their spectra to the profiles. This technique may prove useful to others, even with different applications.

The manganese profile is most uniform in short wave and peaks at 6050 angstroms. By contrast, the caves (organic) profile is more broad and sometimes shows two peaks. It also is more uniform in short wave. The petroleum profile is the broadest of all and peaks on average at 5300 angstroms in both wavelengths. I found both the caves and petroleum profiles are much more consistent in short-wave light, thus I would recommend using short-wave spectra graphs for chemical analysis. The uranium profile peaks at 6200 angstroms and like manganese, tends to be narrow. Both the uranium and rare earth element profiles have multiple short peaks, which are indicative of rare earth element transitions.

Plot Profile of Calcite Samples containing Organic Elements

Plot Profiles of Calcite Samples containing Manganese

Helium Profile

Most samples showed no change in their fluorescence with heating and cooling. However, a few minerals showed changes in color and intensity. These samples were from Franklin, NJ, Silver Crater Mine, Ontario, Atikokan Ontario and Chihuahua, Mexico. I took their spectra and found that most of these minerals emitted more intense light when heated, and a less intense light when cooled. I did not notice any shift in wavelength in any of the spectra. The increase or decrease in brightness may be attributed to a larger or smaller number of electrons in traps in the crystal structure or a change in the activity of a chemical activator. Samples containing manganese tended to become redder when heated and became dimmer when cooled. Samples containing europium were likely to get brighter when heated and also lost their color under white light. One sample containing uranium became brighter under long wave light when cooled.

There is a huge range in fluorescent colors under both short and long wave ultraviolet light, all the way from blue to red. The samples fall into three main color groups, the smallest being the blue/whites, a group of oranges, and a larger group of reds. The blue/whites colors are indicative of areas that may contain organics such as cave environments and petroleum bearing rocks. Most of the reds and oranges appear to be due to manganese (deeper reds) or rare earth elements (orange-pinks), especially uranium. The minerals that fluoresce blue/white tend to show broad spectra. The narrowest spectra are the deep reds.

I would like to thank Leslie Kellman, Jay Sinclair, William Cordua, Judy Ruddock and Art Weinle for donating countless samples for my research. I would also like to thank Ardis Maciolek, my advisor, for giving up time, money, and effort to help me attain success.

To see an expanded version of this research, go to http://north.gp.k12.mi.us/~maciola/webpages/studentprojects.htm. I found this research to be very time consuming. However, the rewards of my research have been overwhelming.

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