Find Block Device

Plug-in your USB stick and find what "/dev/diskN" it is mapped to by opening Terminal (where "N" stands for "disk0", "disk1", "disk2" etc). To do so, please execute:

#diskutil list

This will print out the list of currently mapped devices/partitions. Find the USB using "NAME" column. Then note the corresponding /dev/diskN, where "N" is for index of your disk. For example:

/dev/disk2
   #:                       TYPE        NAME                    SIZE   IDENTIFIER
   0:                       FAT32                               2.0 GB   disk0
   1:                                   USB2                    2.0 GB   disk0s1
In this case "/dev/disk2" is the one we want.

Unmount USB Stick

#diskutil unmountDisk /dev/diskN 

Where /dev/diskN is the one you have found in previous step as per our example it would be "/dev/disk2".

Write ISO to USB

# sudo dd if=/path/to/downloaded.iso of=/dev/rdiskN bs=4k

/dev/rdiskN is the same disk you have found previously, with an r in front. r is for raw disk, as writing to /dev/rdisk2 is much faster than writing to /dev/disk2. You will be prompted for the administrator's password.