Create a bootable SDHC from a Mac

Download alpine rpi file

Prepare SDHC

Insert SDHC card in Mac (if new, it's likely to be formated FAT32)

Open Terminal (Accessories > Terminal) and run the following:

df -h

look for the name of your sdhc device, something like /dev/disk2s1 it's critical you find the correct name, you can loose your hard drive data if you get it wrong)

sudo diskutil umount /dev/disk2s1

sudo fdisk -e /dev/disk2s1

Ignore fdisk error: could not open MBR file /usr/standalone/i386/boot0: No such file or directory

p

f 1

write

exit

Lets remount the disk

sudo diskutil mount /dev/disk2s1

open alpine rpi tar.gz file and expand into a new folder

copy contents of that new folder to card

click eject card in Finder