I suppose armature is the Blender term for a skeleton/ joint hierarchy? In that case you're going to need the
Open Collada plugin. Unfortunately, it only works for Maya 2011 and lower, there is no version for Maya 2012 and 2013. Once activated under Window>Settings/Preferences> Plug In Manager, the .dae format should simply appear in your File>Export - dialogue. For details concerning the options in the export dialogue and troubleshooting, you can also have a look at
this thread, where crisosphinx collected all sorts of tips and common issues.