Are .lib(msvc) files and .a(mingw) files the same?

I read in one of the questions on this site that .a files and .lib files had the exact same con开发者_开发问答tent, but saved under a different name. Is this true? If it isn't true, could you point me to a .lib to .a converter of some sort? Is that even possible? What I am trying to do is get openscenegraph working for mingw (as a cross-compiler), but from what I can see, they only have msvc libraries. I am on ubuntu, so I can't use msvc, but I can use mingw.

I have read that you can just rename them, but this site suggest otherwise

www.inonit.com/cygwin/jni/invocationApi/archive.html