The contacts are stored in a SQLite3 database file so the file format is ".db"
The development tool Android Debug Bridge (ADB) can be used to extract the file from an EMULATOR
ADB can also extract the file from a phone but it must be rooted first AND the ADB drivers must be installed on your machibe as well
(Rooting is NOT for beginners though)
The contacts.db file is stored in the protected system memory, the file path is: