Bad Chemistry in Astronomy Magazine

[pghnative]

The following bit of chemistry is only loosely related to astronomy, but since it is the only topic I'm qualified to post on, I thought I'd indulge myself. :D

In the November issue of Astronomy magazine, there is an article about amateur telescope makers. In a paragraph about optical coatings, the author talks about the chemical additives "Magnesium flouride (MgF) and "Calcium flourite (CaF2)" which can affect the optical properties of lenses. (emphasis added)

There's a lot wrong with that paragraph. MgF doesn't exist, since Mg is divalent and F is monovalent. It exists as MgF2 (correctly called magnesium flouride). Also, changing "-ide" to "-ite" usually means to add an oxygen to the ion. (For instance "chloride" is Cl-, whereas "chlorite" is Cl-O-). So I don't know if the author meant CaOF ("Calcium fluorite") or just meant to call CaF2 "calcium flouride". Since I'm not sure if F-O- ("fluorite") exists, I think the author meant "calcium flouride".

If someone here is more familiar with glass additives, please correct me on this.

[TriangleMan]

Looks like they meant calcium fluorite (http://www.britannica.com/eb/article?tocId=9034679) but it is still CaF2 without an oxygen - fluorite appears to be the mineral's name. Googling calcium fluorite turned up a lot of links on telescopes and lenses.

I agree with you on the magnesium point, it should be MgF2 not MgF.

[Swift]

That was my guess too; the mineral fluorite is calcium fluoride (and I've never seen it called calcium fluorite). MgF2 is a very common optical coating material. I'm not as familar with CaF2 as an optical coating, though it is used as a lens material in various applications (for example, as a UV or IR transparent lens).

(I work for a company that grows various fluoride crystals) :wink: