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FLUORESCENCE IN MINERALS: A BRIEF INTRODUCTION TO WONDERLAND

April 26, 2021

By Peter Rosewarne

Introduction

The branch of mineralogy dealing with fluorescence apparently gained popularity in the 1930s with the availability of battery-powered portable ultraviolet (UV) lamps. The pioneer in producing such UV lamps and using them to prospect for and showcase minerals was Thomas S Warren, after whom the Thomas S Warren Museum of Fluorescence at Sterling Hill Mine Museum in the USA is named.

Those of you who have been paying attention to previous MinChat articles will remember or knew or guessed already that fluorescence is named after the common mineral fluorite, the earliest mineral to have been observed showing this phenomenon. This may even date back to antiquity with Pliny the Elder having remarked upon “chrysolampis”, a stone, “pale by day but of a fiery lustre by night”, which could have been fluorite.

The causes of fluorescence are certain disruptive factors or activators in the crystal lattice. Only about 10 per cent of minerals exhibit fluorescence. Fluorescence is grouped under the umbrella-term luminescence which is a collective term for the ways in which a substance emits visible light under the influence of certain rays. 

Background

And now, as usual, some mildly technical stuff. There are over 500 minerals that exhibit fluorescence, the more common ones including fluorite, calcite, willemite, scheelite, apatite, aragonite, wollastonite and sphalerite. Ultraviolet light comes in short and long wavelengths with more minerals reacting to short-wave than long-wave, while some react to both. Some always glow with the same colour while others are site-specific, e.g. calcite from Franklin is always orange/red. Minerals usually cease to react when the UV source is turned off, while some continue to react for seconds or longer, a property known as phosphorescence.

Some minerals fluoresce even in direct sunlight and do not need a UV light to show this characteristic. For example, fluorite from the Rogerley Mine in Durham, UK, shows striking fluorescence in sunlight, changing from a deep green to a deep blue, as shown in Figures 1 and 1b, respectively. In the fluorite article of January-February 2021 this effect was mistakenly called dichroism.


Figure 1


Figure 1b

Fluorescence can be a useful way of determining if a mineral specimen is a fake, as glue will show up with a different response to the mineral. It can also be used to determine whether gems are genuine. 

The Fluorescent Mine

OK, that’s some technical stuff out of the way, from a non-expert on the subject, and a short list of common minerals that exhibit fluorescence. So now for something completely different; instead of looking at individual minerals and their fluorescent properties, we are going to start by looking at a whole mine that fluoresces! For this we are going to the Sterling area of New Jersey in the USA, which has been dubbed the Fluorescent Capital of the World.

The mineralogy of the Sterling Hill and Franklin ore body is unique in that the main zinc ore minerals are franklinite (zinc-manganese-iron oxide), willemite (zinc silicate) and zincite (zinc oxide). The two mines have yielded about 30 million tonnes of ore over two centuries of mining, with the Sterling Mine closing in 1986. However, the area is still very much open and popular with scientists, rock-hounds and the general public in the form of the Sterling Hill Mining Museum at Ogdensburg (https://www.sterlinghillminingmuseum.org/warren-museum-of-fluorescence).

These visitors (c.40 000 a year) are not only interested in the mining history of the area and the unique mineralogy but also the colourful fluorescence exhibited by both individual mineral specimens and the spectacular fluorescence exhibited by the remaining in situ ore and associated minerals in the Sterling Hill Mine.

Figures 2 to 5 illustrate some of the wonders to be seen at the site, showing various faces, tunnels and stopes of the Sterling Mine under short-wave UV light, with calcite being orange and red, willemite green and hydrozincite blue.


Figure 2 - Stirling Hill mine rainbow room


Figure 3 - Stirling Hill mine tunnel


Figure 4 - Stirling Hill quarry wall


Figure 5 - Stirling Hill stope

Figure 6 shows a small selection of Sterling Hill minerals under UV light from the Thomas S Warren Museum of Fluorescence, while Figures 7 and 8 show typical Sterling Hill mineral groups of willemite and calcite under normal and short-wave UV light. In Figure 8b the franklinite shows up black as it doesn’t fluoresce. The current list of fluorescent minerals found at Sterling is 89.


Figure 6


Figure 7 - Willemite and calcite under normal UV light


Figure 7b - Willemite and calcite under short-wave UV light


Figure 8


Figure 8b - the franklinite shows up black as it doesn’t fluoresce

Concluding Remarks

This is a very short article that barely scratches the surface of the subject and has a fairly narrow focus both site and mineral-wise. However, if, like me, you weren’t previously “into” fluorescent minerals, hopefully, like me, you will be now.

References

The Mineralogical Record. (2016). Mineral Collections in the American Northeast. Supplement to The Mineralogical Record, July-August 2016. Tucson.

Fisher, J. et al. (2006). Fluorite: The Collector’s Choice. Lithographie. Connecticut.

Staebler, GA and Wilson, WE. Eds. (2008) American Mineral Treasures. Lithographie. Connecticut.

Heritage Nature and Science Auction. (2014). Fine Minerals, Gems and Lapidary Art. Catalogue, September 28. Dallas.

 

TRIALS AND TRIBULATIONS WITH CUT GEMSTONE HEATING

March 25, 2021
Duncan Miller

Inspired by the dramatic change in colour of the large tourmaline illustrated in last month’s Mineralogical Chatter, that went from autumn brown to a purplish-pink on heating by the client for whom I had cut it, I decided to experiment myself. A friend lent me a small ‘enamelling’ kiln; I bought a suitable crucible from jewellers’ supplier Lipman & Son in Cape Town (https://lipmanson.co.za/); and Ian Lipman generously gave me jewellery casting investment powder to protect...


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Six of the Best Specimens in the Mineral Kingdom!

March 25, 2021

By Peter Rosewarne

Introduction

Have you ever wondered if there was a specimen out there that was the world’s best, or what the best six or ten mineral specimens ever discovered are considered to be? I thought it might be a bit of fun to put together a “Six of the Best” of the mineral kingdom based on expert opinion in respected publications, such as The Mineral Record and its supplements, Masterpieces of the Mineral Kingdom, and American Mineral Treasures. Some of these discoveries g...


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THE MOST DIFFICULT JIGSAW PUZZLE OF ALL TIME

February 24, 2021
by
Duncan Miller

Imagine a jigsaw puzzle the size of the Earth, with most of the pieces missing. And those that aren’t missing are moving around all the time. This is the task that confronts some ambitious geologists. It is important because it explains why there are oceans and mountain chains, and why we may find rocks of similar ages and composition on far-flung continents. It also satisfies human scientific curiosity, and keeps some people employed and off the streets.

Until the mid-1960s...


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Botryoidal Minerals: A Colourful Trip Around the Mineral Kingdom

February 24, 2021

by
Peter Rosewarne

Introduction

My previous MinChat article on fluorite described a colourful trip around the world. In this article we take a colourful trip around the mineral kingdom, using minerals with a botryoidal habit as the guide. The idea came from the supplement to The Mineral Record of January-February 2020 on Mineral Collectors in Arizona, with the focus of one of the collectors being on botryoidal mineral specimens. The term botryoidal is derived from the Greek word botryios or ...


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FLUORITE - A COLOURFUL JOURNEY AROUND THE WORLD

January 15, 2021

by Peter Rosewarne

Fluorite: cubic, common, cheap (comparatively, but can be costly), contains calcium, and colourful, are some of the "C" words that can be used to describe this mineral. While good specimens of fluorite from classic localities aren’t cheap, most are cheaper than good specimens of ‘higher-end’ minerals such as azurite, dioptase, tourmaline and beryl and it is possible to build up a good collection of fluorites from worldwide localities. You are also likely to get a nice-...


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SAMS outing to the Springbok area, September 2020

December 4, 2020

Lesley Andrews


Jubilee copper slag dump, near Concordia

Towards the end of September, Richard and I met up with some members of SAMS (South African Micromount Society) in the Northern Cape. The Society is based in Gauteng, and the trip included site visits en route from Johannesburg. The Chairman of SAMS, Patrick Barrier, and Linda Stone, the President of FOSAGAMS, also joined the outing.

In the Northern Cape we stayed in accommodation at Springbok and Nababeep. This area is well-known for cop...


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Springbok Recce: Geology, Mining Heritage (and Wild Flowers)

December 4, 2020

By Peter Rosewarne


Figure 1 The Matzikammaberg at Vanrhynsdorp

This trip had its beginnings during the Lockdown with reading up on some books on South Africa’s mining heritage, geological sites and geological journeys. With the relaxation of travelling restrictions and reports of a bumper flower season in Namaqualand, I decided on the spur of the moment to do a trip to the Springbok area, which is rich in sites of geological and mining interest. My wife and I were going to go but, in the we...


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SOME UNUSUAL POLISHED SLABS

October 26, 2020

Peter Rosewarne

Polished slabs and spheres don’t usually figure highly in my wish-list of mineral specimens but, over the years, some colourful and interesting ones have caught my eye and have been added to the Rosey Collection. This short article highlights some of what I hope you will agree are both unusual, interesting and colourful polished slabs from various localities around the world. The slabs very briefly described and illustrated herein are Sonora Sunrise and Laguna Agate from Me...


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PICKY PIGEONS PREFER POLISHED PEBBLES

October 26, 2020

Lesley Andrews

I am the proud owner of two stone plants which I keep on the stoep table - these are decorated by a surface layer of small tumbled semi-precious stones. Recently I was astonished to see a threesome of Cape Turtle Doves on the table carefully picking out some of the stones, passing them to each other, rolling them around in their beaks and putting them down carefully all over the table. I knew that many birds eat grit, but why this preference for my ornamentals?


The Cape Turtle Do...

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