Minerals/Halogens

The fluorite crystal is just over 1 cm and is rimmed on one side with sparkling pyrite. Credit: Robert Lavinsky.

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.

Fluorines

This is a phase diagram for fluorine versus pressure. Credit: U.S. Energy Research & Development Administration (ERDA).

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.

Chlorines

This 1975 phase diagram of chlorine is generally incomplete, reaching at most 250 kbar (25 GPa) and thus lacking many high-pressure metallic phases. Credit: David A. Young.{{free media}}

This phase diagram was taken from "Phase Diagrams of the Elements", David A. Young, UCRL-51902 "Prepared for the U.S. Energy Research & Development Administration under contract No. W-7405-Eng-48".

Technology

Main article: Technology

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. Credit: Canon.{{fairuse}}

"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."

Hypotheses

Main article: Hypotheses

1. Although halogens form ionic bonds, natural compounds exist that allow halogen vapors.

See also

• Ultraviolet astronomy