export a single calendar from iCal

Click on calendars, select calendar wchich you want to export then go to File>Export>Export... and save file on the desktop and then send file via email.

But if by calendar you mean calendar Event, then double click on event and in "Add Invitation" field add email of the person which should have access to your event.

Select the specific Calendar - go to file in the menu bar - click Export. It will save an ics file to any destination you choose.

Are you sure you clicked and selected the specific calendar and not just checked it?