XML has two main MIME types: text/xml and application/xml. I'm not sure which is to be used for which, but I think text/xml is for XML files that are pure data, while application/xml is for XML languages that actually instruct an app to do something.

Example for text/xml:
Code:
<storelist>
  <item>
    <name>Chair</name>
    <amount>32</amount>
  </item>
  <item>
    <name>Table</name>
    <amount>5</amount>
  </item>
</storelist>
Examples for application/xml are XHTML and SVG. Those have their own MIME types though: XHTML uses application/xhtml+xml and SVG uses image/svg+xml.

I'm sure this is explained in greater detail in the XML specification.
www.w3.org