Luminescence in Minerals
The ethereal flicker of a filmy veil deep within the Marianis Trench, rocks that glow with pastel shades of peach and mustard yellow, lit as though fired from within, by fairy fire. It’s not the fantasy of a fevered brain, but rather luminescence cast forth by chemical and molecular reactions. Purely natural phenomenon that we will examine from a mineralogical perspective in the coming video. From a mineralogical perspective, you as a collector of crystals and minerals will be astounded by what you learn and see.
Fluorescence and Phosphorescence
So to begin we need to look at the overall concept that is neatly encapsulated within the term of luminescence. It encompasses a range of beautiful phenomenon. Luminescence refers to the emission of light by a substance that’s not been heated. This phenomenon can be observed in a variety of materials, including minerals and living organisms. The light’s excitation wavelength is shortwave – of higher energy, and the fluorescent or phosphorescent wavelength is of a longer wavelength or lower energy.
Specifically in this discussion we’re looking at minerals. Broadly speaking, there are different types of luminescence in minerals, with fluorescence and phosphorescence being the two most commonly discussed. Both types of luminescence involve the absorption of energy and subsequent emission of light, but they differ significantly in their duration and the mechanisms involved.
Fluorescence is the immediate emission of light upon exposure to an external energy source, while phosphorescence involves a delayed emission that can last from seconds to hours or even longer. The following discussion will delve into these two types of luminescence, explain their differences, and provide a closer look at how these phenomena manifest in specific minerals such as fluorite, calcite and scapolite. It is those minerals that we at the Dark Star crystal Mines most commonly encounter in a fluorescent sense, a night trip with UV light on our claim can lead us into an eerily glowing fissure that suggests an alien world.
Fluorescence in Minerals
Fluorescence occurs when a mineral absorbs ultraviolet (UV) or other high-energy light and immediately re-emits that energy as visible light. The process begins when the mineral’s atoms or molecules are energized by photons from an external light source, causing electrons to jump to higher energy levels, in other words they move to higher orbitals in the electron shell arrangement. These excited electrons then lose their Mo-jo, returning to their lower energy states releasing the excess energy required to keep them in the higher orbitals as visible light. You will notice that a light that excites starts in the ultraviolet wavelentgth and comes back as red or yellow – the wavelength has lengthened. This emission of light happens almost instantaneously and ceases the moment the external energy source is removed.
Fluorescent minerals often display vivid and colorful emissions. The exact color depends on the chemical composition of the mineral and the specific wavelengths of energy it absorbs and emits. Certain elements are known to enhance the effect, they are called activators. Examples of activating elements are manganese, chromium and iron 3+, and then there are the quenchers that resist activation. Examples of quenchers are copper, nickel and iron 2+
Phosphorescence in Minerals
Phosphorescence, unlike fluorescence, involves the delayed emission of light after the excitation energy has been removed. When a mineral is exposed to UV or visible light, it absorbs energy, but in phosphorescent materials, the electrons involved in the excitation process do not immediately return to their ground states. Instead, the excited electrons temporarily become trapped in metastable states. Over time, the electrons will return to their lower energy states, gradually releasing the stored energy as visible light. This process can take anywhere from a few seconds to several hours, or even longer, depending on the material. Understanding that more energy cannot be given off than has been added, the glow of phosphorescence tends to be fainter than the immediate flash of fluorescence. No more energy can be given off than was added, but the balance can be maintained by a slower fainter release.
The Key Difference Between Fluorescence and Phosphorescence
The primary distinction between fluorescence and phosphorescence lies in the duration of the light emission. Fluorescence is a fast and immediate process, where light is emitted as soon as the mineral absorbs energy, and stops as soon as the energy source is removed. On the other hand, phosphorescence is a delayed emission, with light continuing to be emitted for an extended period after the excitation source is no longer present.
Luminescent Minerals: Fluorite, Calcite, Sphalerite, and Scapolite
In the area of the Bear Lake Diggings certain of the minerals that are found exhibit striking luminescent properties, and most prevalent amongst them are fluorite, calcite and scapolite, and of course there is also the sphalerite that we’ve found in the Niagara Falls dolostones. Each of these minerals exhibits either fluorescence, phosphorescence, or both, and their luminescent behaviors can vary depending on their chemical composition, crystal structure, and the conditions under which they are examined. An example of this would be the fluorescence in calcite, with a zinc component calcite’s fluorescence will be green, but with manganese it will be red.
Calcite
The luminescent properties of calcite are well known and there’s no shortaqge of this substance in the Bear Lake area, it is the primary in-filling of the local vein dykes and as crystal and mineral collectors can attest, in mass, calcite is somewhat unremarkable, but in its crystal spires and glowing with its fluorescent qualities its like the towers of a fantasy castle. Calcite (CaCO₃) exhibits both fluorescence and phosphorescence, although its fluorescence tends to be weaker than that of fluorite. Calcite can fluoresce in various colors, including red, orange, and green, under UV light. The mango-peachy glow from the spiky specimens that we found near Chaffey’s locks is other-worldly. It is the presence of specific impurities such as manganese or uranium that gives calcite its special glow. Zinc and cobalt taints are known to produce a serene bluish glow in those unusual calcites, though we are yet to see those on our claim. Calcite’s phosphorescence is typically more pronounced than its fluorescence. It lasts from several seconds to a couple of minutes. The characteristic glow after the excitation source is removed is often green or yellowish.
Fluorite
Fluorite (CaF₂) is one of the most well-known fluorescent minerals. It’s properties were discovered by George Stokes in 1852 and it was this that led to the law of Stokes shift, or the basic mechanisms of fluorescence as we know it, the difference in wavelength between when a molecule absorbs light and when it emits light.
Fluorescent minerals are highly prized by crystal and mineral collectors for their vivid colors which can range throughout the spectrum, depending on the trace elements in the crystal lattice. Some specimens show a strong glow when exposed to short-wave UV light. Amongst the most notable of Ontario fluorite’s are those from the Rogers Mine in Madoc. They appear as beautiful clumpy green crystals that fluoresce etherial shades of violet and when tumbled, that violet is interspaced with streaks of white fracture and ghostly floating images within the rock. Mustard planes also striate the innards of the bigger stumps, possibly from the contamination of its companion barite.
Barite and celestite – a strontium ore, both contain rare earth elements and these can accentuate the light show. Evolving from ocean brines the two elements tend to back the fluorite crystals from the Madoc area and the distinctive cross hatching of barite with its of europium and cerium are said to also appear as contaminants in the fluorite crystals. Those two elements are responsible for fluorite’s soft mauves and deep raspberry purples under UV light..
In addition to its fluorescence, fluorite can sometimes display a subtle form of phosphorescence, with a faint glow lingering after the UV light source is removed, though this is less common than its fluorescence. One of the more impressive fluorescence transformations is that of chloraphane which being purple in color fluoresces a vivid emerald green.
Scapolite
Scapolite is a group of isomorphous silicate minerals. They exist along a continuum between meionite and marialite. Scapolites are said to be less commonly known for their luminescent properties, but the varieties that we are finding in the roadcuts of Monmouth township fluoresce an incredible yellow – reminiscent of the glowing embers in a camp-fire. Some suggest the color is due to the scapolite’s S2 content. The fluorescence of scapolite is typically weak compared to that of fluorite or sphalerite, and it is often observed in pale blue or green hues. It’s said that cerium is the element responsible for this cooler hue and though we are finding cerium-rich monazite in some of our Bear Lake vein dykes, we are yet to see that cerium-blue fluorescence. Phosphorescence in scapolite is relatively rare though some specimens may glow faintly for a short period after excitation. Local road cuttings are a good source of rough scapolite material, I believe by the fluorescent reaction that it is the meionite that predominates.
Conclusion
Luminescence in minerals, including fluorescence and phosphorescence, is a fascinating phenomenon that adds to the allure and scientific interest of certain species. Fluorite, calcite and scapolite are just a few examples of minerals that exhibit these luminescent properties, but in a biological sense there’s also chemiluminescence which is generated by a chemical reaction. This is commonly seen in fungi, fireflies and deep sea creatures. I suppose a nightclub can sum it up quite succinctly. Glow sticks are giving their light by way of a chemical reaction. Two chemicals are mixed and they begin to glow. Light is not added to cause the effect. The body paints and glowing makeup are an example of fluorescence. UV light is needed to trigger their properties and what is returned from the short wave, high energy excitation wavelengths are the longer wave low-energy glows. Now the exit sign has a phosphorescence. Triggered by the light it glows for some time when the UV light has stopped exciting it. And so as the exit makes its glowing presence in the dark, so to do we at Dark Star Crystal Mines make our exit on this video. Be sure to visit our webside and subscribe. We will, or already have local fluorescent minerals up for sale including those amazing scapolites and peach calcites.