how to change a mime type for a file

[Giuseppe Sacco <giuseppe eppesuigoccas homedns org>]

Hi all,
I have two gnumeric files in my ~/Desktop directory. One is shown with
gnumeric icon, the second one with a generic gnome icon. (I am using
gnome 2.10.1 on debian.)

If I see the file properties I notice the they have different mime
types. The first one is application/x-gnumeric, the second one is
application/x-font-tex-tfm. Of course when I double click on the second
I got a message (from nautilus?) that says the file is really a "tex
font" even if the name ends in gnumeric, do nautilus refuse to open it.

What should I do? How do I change the mime type of the second file?

Thank,
Giuseppe

P.S. Please CC me since I am not subscribed to this list.