Fluorescent Minerals
Certain minerals are capable of absorbing invisible ultraviolet light with a wavelength from 200nm to 400nm and give off visible light with a wavelength from 400 to 700nm and “glow” in the dark, they fluoresce.
What makes a mineral glow?
Most fluorescent minerals require an activator that initiates fluorescence. The activator is a small amount of a certain chemical element or impurity having been included in the original crystal structure in different places. However, impurities of some elements such as iron and copper deter the fluorescence in minerals.
The Process:
Fluorescent minerals contain certain atoms with electrons that are taken up to a higher excited energy levels by absorbing energy from the incoming ultraviolet light (1). These electrons instantly fall back to their original energy levels, giving off energy in form of visible emitted light (3). This takes place in a very small fraction of a second. We see only the resultant visible light emitted as long as the atoms are exposed to the ultraviolet light. Depending on the energy released when electron returning to their original level (2), minerals exhibit different fluorescence colors.
Fluorite
Halides
CaF2
The common blue fluorescence seen in fluorites, which is responsible for the naming of the phenomenon of fluorescence itself in the year 1852 by George Gabriel Stokes, has been attributed to the presence of inclusions of europium in the crystal.
Calcite (Mangano-calcite)
Carbonates
(Ca,Mn)CO3
New South Wales, Australia
Some minerals which do not normally fluoresce will sometimes do so because of an activator. For instance, most forms of calcite do not fluoresce. Yet, if a small amount of manganese is present in the mineral, it acts as an activator and causes the calcite to fluoresce red. The brilliance of the fluorescence varies with the amount of manganese.
Autunite
Phosphates
Ca(UO2)2(PO4)2·10-12H2O
USA
In autunite, the activator element Uranium, in the form of the uranyl cation, causes a yellow-green fluorescence. Unlike manganese, the uranyl ion in minerals is quite insensitive to its atomic environment, and thus a similar color of fluorescence appears regardless of the mineral species.
Opal
Tectosilicates
SiO2·nH2O
Nevada, USA
Opal (var. Hyalite)
Tectosilicates
SiO2·nH2O
North Carolina, USA
Opal and Hyalite, a form of opal with a glassy and clear appearance, show a bright-green fluorescence due to the presence of Uranium as an activator.
Calcite with Willemite and Franklinite
CaCO3, Zn2SiO4, ZnFe2O4
New Jersey, USA
Willemite with Calcite and Franklinite
Zn2SiO4, CaCO3, ZnFe2O4
New Jersey, USA
This is a classic combination of Calcite, Willemite and Franklinite from a Zinc and Manganese Ore Deposit at Sterling Hills in New Jersey (USA) renowned for its bright fluorescence colors in some minerals due to the presence of Manganese as an activator. The tan-colored Willemite exhibits a bright green fluorescence while the white-colored calcite exhibits a pink fluorescence. The iron-rich mineral Franklinite is not fluorescent and is represented by the dark areas in the photo.
Scapolite
Tectosilicates
(Na,Ca)4Al3Si9O24Cl
Québec, Canada
Scapolite from Quebec in Canada fluoresces a vivid orangeish-yellow color, probably activated by sulfur or uranium impurities.