Halogens are elements in column 7A of the periodic table. They occur as a principal component in a variety of minerals.
On the right, is an example of almost completely clear fluorite (CaF2).
Impurities can give color. Some halogen minerals are called halides.
Although they do not occur naturally on the surface of the Earth, the phase diagram on the right shows temperatures and pressures for α-F (monoclinic) and β-F (cubic).
Fluorine-containing minerals are those that may provide a commercially viable source for the element either here on Earth or elsewhere.
Tysonite, or fluocerite, is a lanthanide fluoride, usually CeF3, for 75 atomic percent fluorine. It occurs in pegmatites on Earth.
In terms of atomic percent, fluorite (CaF2) is 66.7 % fluorine. It occurs on Earth usually as a hydrothermal deposit.
"Fluorite occurs in blue, purple, white, yellow, and colorless varieties. From field relationships the crystallization order was determined to have been blue and purple fluorite, which are commonly interlayered, followed by white, and finally yellow and colorless varieties."
"Throughout most of the fluorite zone purple is the dominant, and commonly the only, color exhibited by fluorite, but in the central parts of the field green fluorite is quantitatively important, whereas at the edges of zone the fluorite is amber in color."
Fifth down on the left is a crystal of rare black fluorite.
Cryolite (Na3AlF6) is 60 % fluorine. It occurs on Earth primarily in pegmatites.
Halite is probably the most common mineral containing chlorine at 50 at %. It is a cubic mineral usually found in arid locations on Earth. Occurrences have clear, white, purple, blue, yellow, orange, and red varieties.
Bromyrite, or bromargyrite, is a cubic silver bromide mineral (AgBr) that is 50 at % bromine.
The image on the right shows a butterscotch colored bromargyrite cube from Broken Hill, New South Wales, Australia.
Iodyrite (AgI) may be the most common mineral with large amounts of iodine found on Earth. It is 50 at % iodine.
On the right are twinned iodyrite, or iodargyrite, crystals are within a rock sample from Schöne Aussicht Mine, Dernbach, Neuwied, Wied Iron Spar District, Westerwald, Rhineland-Palatinate, Germany.
All of the known isotopes of astatine are very short-lived. It occurs naturally in minerals such as uraninite as a decay product of uranium.
"If you hold a prism up against sunlight, a rainbow spectrum will appear. This is due to the fact that different wavelengths of light refract – or bend – at different points within the prism. The same phenomenon occurs to a lesser degree in photographic lenses, where it is known as chromatic aberration. It's most noticeable in photographs as colour fringing at the edges of objects. Combining convex and concave lenses helps to correct the problem but does not entirely resolve it."
"Fluorite, which boasts a very low dispersion of light, is capable of combatting the residual aberration that standard optical glass fails to eliminate. Canon succeeded in artificially creating crystal fluorite in the 1960s, producing the first interchangeable SLR lenses with fluorite elements. In the 1970s, Canon achieved the first UD (Ultra Low Dispersion) lens elements incorporating low-dispersion optical glass. This technology was further improved to create Super UD lenses in the 1990s. A combination of fluorite, UD and Super UD elements are used in many of today's super-telephoto L series lenses, telephoto zooms and wide-angle lenses."
- Although halogens form ionic bonds, natural compounds exist that allow halogen vapors.
- David A. S. Palmer and Anthony E. Williams-Jones (1 August 1996). "Genesis of the carbonatite-hosted fluorite deposit at Amba Dongar, India; evidence from fluid inclusions, stability isotopes, and whole rock-mineral geochemistry". Economic Geology 91 (5): 934-50. doi:10.2113/gsecongeo.91.5.934. http://www.researchgate.net/profile/Anthony_Williams-Jones/publication/235451415_Genesis_of_the_carbonatite-hosted_fluorite_deposit_at_Amba_Dongar_India_evidence_from_fluid_inclusions_stability_isotopes_and_whole_rock-mineral_geochemistry/links/54ceb1170cf29ca810fcad30.pdf. Retrieved 2015-07-27.
- F. J. Sawkins (1 March 1966). "Ore genesis in the North Pennine orefield, in the light of fluid inclusion studies". Economic Geology 61 (2): 385-401. doi:10.2113/gsecongeo.61.2.385. http://economicgeology.org/content/61/2/385.short. Retrieved 2015-07-27.
- Canon (2015). "Canon Fluorite and UD Lenses". United Kingdom: Canon. Retrieved 2015-07-27.