Ran into the following error message while installing the gem. I copy and pasted files to ext directory. Can you please help me out on this?

Building native extensions. This could take a while...
ERROR: Error installing content_type:
ERROR: Failed to build gem native extension.

    /usr/local/rvm/rubies/ruby-1.9.3-p392/bin/ruby extconf.rb

checking for magic.h in /opt/local/include... no
checking for magic_open() in -lmagic... no
creating Makefile

make
compiling content_type.c
content_type.c:2:10: fatal error: 'magic.h' file not found

include <magic.h>

     ^

1 error generated.
make: *** [content_type.o] Error 1