The Mineralogy of Nova Scotia

FLUORITE

Introduction

Fluorite is a common mineral that is popular with collectors around the world. It forms well formed crystals, often of large size, and in probably a wider variety of colors than any other mineral. Sadly, fluorite from Nova Scotia is very modest compared to many other places, and is not likely to interest most fluorite collectors. Nonetheless, we do have enough variety to demonstrate an interesting variety of shapes and colors within the species.

Crystal Forms

Fluorite is an isometric mineral and is typically found as cubes. Though octahedrons are possible, care must be taken when identifying octahedral faces, because fluorite also cleaves into octahedral shapes. Over the years, I've recorded four other forms found as small faces modifying otherwise cubic crystals. These include the dodecahedron, hexoctahedron, trapezohedron, and tetrahexahedron. The graphic below shows what these forms look like as a pure form and as a modification of a cube. In fact, most of those shapes (with the exception of octahedron and dodecahedron) actually represent a family of different forms with varying steepness between the faces. I have not measured any of these fluorites to determine the Miller indices of the more complex forms.

A table showing eight different forms possible in fluorite. In each pair of drawings, the right figure shows the pure geometric form and the left figure shows that form slightly modifying a cube. The lighter colored shapes have been found in Nova Scotia.

Simple sharp cubes of purple fluorite from East Kemptville.

A cluster of crystals with dodecahedral modifications.

A rough tetrehexahedron from East Kemptville. Nearby crystals were unmodified cubes.

Cubes modified by tetrahexahedrons, from near Chester.

Cubes modified by trapezohedrons, from near St. Margarets Bay. The corner shows three modifying faces, but one is much larger then the other two.

Intensely colored crystal with the corners modified by trapezohedrons and rough tetrahexahedrons. Note how the edges between the three faces of the trapezohedron are in line with the cube edges. That is key to differentiating it from the trisoctahedron.

A locality near Chester has produced some attractive fluorite. It appears to have formed in two generations. The first generation consists of small sharp crystals. They form cubes and are often modified with a hexaoctahedron. The crystals are small, most less than a millimeter, and grade from colorless to purple. The second generation of fluorite forms larger stepped crystals. Some of the crystals show only minor stepping while others are completely rounded masses. In some cases, the fluorite forms botryoidal layers. The earlier figure shows both the hexoctahedral and stepped crystals.

Colors

Perhaps the most remarkable feature of fluorite is the variety of colors that it can display. The most common color is purple. Specimens from the granites of the South Mountain batholith are most commonly this color. The color saturation ranges from nearly colorless, to intense deep purple. Fluorite was abundant at East Kemptville and that material was typically purple in a variety of saturations. Other locations that have produced good specimens of purple fluorite include Chester and Fall River.

Purple fluorite from Chester that is forming cauliflower-like mounds.

Yellow fluorite is also known from several localities. East Kemptville produced a few specimens of yellow crystals associated with siderite. Specimens from St Margarets Bay area (I don't know the exact location) are yellow with a glassy luster. And amber yellow material is reported from Spicer's Cove (Felderhof 1978), but I have not seen a good specimen. That material tends to be massive, forming narrow veins fillings, and is very crumbly.

Yellow fluorite crystals from East Kemptville.

Both purple and green fluorite is reported from several locations in Cape Breton. At MacKenzies River, How (1869) recounts second hand information of blue octahedral crystals up to an inch across! Unfortunately, this locality is now within the Highlands National Park.

There are reports of fluorite in shades of green and blue from various locations, but I have not seen good crystals. I'm particulary intrigued by blue material and detail a couple localities below. First, Honeyman (1867) reports,

"On the western side of Lochaber Lake there are magnificent exposures of the brownish red strata, in the course of a small brook that runs enters the lake. To the south of the brook there is a thick bed of laminated limestone, altered and contorted, containing blue fluor spar."

Another interesting, yet mysterious occurrence is that of small blue crystals at Plaster Cove, Inverness County, described by How. In his manuscript, he first describes other minerals "west of Plaster Cove", and then the fluorite "nearer the Cove", so presumably it is immediately west of the community. Plaster Cove is now known as Port Hastings. Felderhof lists a Plaster Cove fluorite but could not find any and assumes it was in eroding gypsum. He also quotes Coste (1888), "Fluorspar of a beautiful blue colour is found at Plaster Cove, Richmond County" - note that the county seems to be incorrect. Felderhof includes a seperate listing for MacMillan Point (he could also find nothing there) and quotes Campbell (1947), "Small veinlets of whitish crystalline barytes may be seen in Horton sandstone to conglomerate along the shore just North of Port Hastings. Just south of this point, blue crystals of fluorite may be found in limestone cuttings along the C.N.R. railroad." I suspect these reports are related, as MacMillan Point appears to be within the limits of the current Port Hastings, but I don't know its exact location.

Brown fluorite is reported from Little River (Felderhof 1978).

Some very dark crystals were found in an aplite dyke in the Bayers Lake 2018 expansion area. The smallest crystals showed a dark purple color but larger crystal fragments appeared nearly black. Black fluorite is sometimes called 'fetid fluorite' or 'stinkpsar' for the smell created when it is crushed (Schmedt auf der Günne, et al., 2012). It has been determined, from other localities, that the black color is due to radiation. The radiation creates fluorine gas and clusters of metallic calcium. The fluorine gas is released in crushing and reacts with oxygen and water in the surrounding air to produce ozone, and thus creating the 'fetid' smell. The metallic calcium is responsible for the black color. I have not tested this local material for smell, but the color certainly matches and the expectation of radiation is very reasonable. Piers (1912) also reports purplish-black fluorite from the Reeve's pegmatite near New Ross.

A fluorite cleavage octahedron from Bayers Lake. The light areas in the photo are surface reflections from the strong lighting and a couple purple internal reflections can also be seen. In the hand, however, the piece is black.

Color Zoning

Fluorite shows a strong tendancy towards color zoned crystals. Again, there are several examples from Nova Scotia. A few are shown below.

Strongly color zoned fluorite.

Remains of a large fluorite that was growth limited by the narrow vein. The interior is pale green and the outer rind is purple.

From Chester, a few crystals showed the edges of a cube, outlined in purple, appearing twice as the crystal grew, inside an otherwise colorless cube. In the photo below, I was forced to lightly oil the crystals to get a clear shot of the phantoms inside. The effect is much more impressive in person because the phantoms are three dimensional and as you turn the specimen you can get some very interesting views.

Double phantoms from near Chester.

Fluorescence

The words fluorite and fluorescence share the same roots, as fluorite is known to frequently fluoresce and often very brightly. Material from Chester fluoresces a dull white color on dimly red fluorescent quartz.

Fluorite from Chester in visible light (top) and fluorescing dull white under ultraviolet light (bottom).

Associated Minerals

Shown below is a colorful specimen from East Kemptville. In this case the fluorite is color zoned, with purple edges. The crystals are studded with small pyrites, and associated with orange stilbite/stellerite. Fluorite was also often associated with siderite at the mine.

Pyrite studded fluorite with stilbite/stellerite.

At Fall River, Halifax Co., the fluorite occurs as small purple cubes associated with quartz, barite and cerussite in granite. At Cheverie, fluorite is found in small quantities in gypsum/anhydrite and sometimes associated with danburite and dolomite.

Conclusion

Fluorite would have to be listed as a common mineral from Nova Scotia, but good specimens are rare and significant display specimens are unknown. Nonetheless, there are some interesting crystals found in small quantities. These offer a variety of habits and colors making it an interesting mineral to collect and study.

Acknowledgements

Thanks to the landowners in Chester for allowing us access to collect those interesting fluorites. Also thanks to the staff at the East Kemptville mine for allowing access to that site for collecting.

References

Felderhof, G.W. (1978) "Barite, Celestite, and Fluorite in Nova Scotia", N.S. Dept. Mines. [Online 2014]

Honeyman, D., (1867) "Geology of Antigonish County, N.S.", Nova Scotia Institute of Science, vol. 1, part 4. [Online 2015]

How, H. (1869) "The Mineralogy of Nova Scotia. A Report to the Provincial Government.", Charles Annand (Publisher), Halifax, Nova Scotia. [Online 2014]

Palache, C.,Berman, H. and Frondel, C. (1951) "The System of Mineralogy", Volume 2, 7th Edition, John Wiley and Sons.

Piers, H. (1912) "On the Occurrence of Tin in Nova Scotia", Proceedings & Transactions of the Nova Scotia Institute of Science, vol. 12, pg. 239-249. [Online 2018]

Schmedt auf der Günne, J., Mangstl, M., and Kraus, F. (2012) "Occurrence of Difluorine F2 in Nature - In Situ Proof and Quantification by NMR Spectroscopy". Angewandte Chemie International Edition, 51(31), 7847–7849.

Disclaimer: This page is intended for information purposes only. The localities described are not necessarily open to collecting and are not necessarily safe.