Minor Description
I found several GZip mime types (which were supported by our group till we began using Tika) which aren't listed in the Tika registry.
Now, I am not sure if they are legit or not, and I think that a Tika member will be able to investigate and decide if they should enter as mime types or aliases to gzip.
These are the types:
application/x-gunzip
application/gzipped
application/gzip-compressed
gzip/document
They can be found listed here:
http://mimeapplication.net/x-gunzip