RMagick LoadError

I installed RMagick 2.9.1 and tried to test RMagick code below.
irb -rubygems -r RMagick
But I got an error like below.

/usr/local/lib/ruby/gems/1.8/gems/rmagick-2.9.1/lib/RMagick2.so:
libMagickCore.so.2: cannot open shared object file: No such file or
directory -
/usr/local/lib/ruby/gems/1.8/gems/rmagick-2.9.1/lib/RMagick2.so
(LoadError)
from
/usr/local/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:36:in
require' from /usr/local/lib/ruby/gems/1.8/gems/rmagick-2.9.1/lib/RMagick.rb:11 from /usr/local/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:36:in gem_original_require’
from
/usr/local/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:36:in
require' from /usr/local/lib/ruby/1.8/irb/init.rb:252:in load_modules’
from /usr/local/lib/ruby/1.8/irb/init.rb:250:in each' from /usr/local/lib/ruby/1.8/irb/init.rb:250:in load_modules’
from /usr/local/lib/ruby/1.8/irb/init.rb:21:in setup' from /usr/local/lib/ruby/1.8/irb.rb:54:in start’
from /usr/local/bin/irb:13

I searched and referred
http://rmagick.rubyforge.org/install-faq.html#loaderror
So I inserted code below to “.bash_profile”
export LD_LIBRARY_PATH=/usr/local/lib

But still same error occur ande doesn’t work.
Any advise?