Contacts can be exported in vCard format; the filename ends with.vcf.
To export contacts

1. Click Address Book

   

2. From the Groups pane, choose the group that contains the contacts that you want to export.
   Select Contacts if you want to export all of the contacts in the Address Book.

   

3. Optionally, click to select the individual contacts that you want to export.
   To select multiple contiguous items, select the first item, hold down the Shift key, and then click the last item. To select multiple non-contiguous items, hold down the Ctrl key and click on each of the items that you want to select.

4. From the Export drop-down list, choose Export all or Export selected

   

5. Choose where to save the exported file if prompted; otherwise, check the Downloads folder on your computer for a file called contacts.vcf