“chef_gem” and  “gem_package” resources are used to install Ruby gems. Every system where CHEF Client is installed has two versions of Ruby running. One is a system-wide instance of Ruby and the other is the one available only with Chef Client. “chef_gem” resource is used to install Ruby into Chef Client instance of Ruby and “gem_package” resource to install Ruby into a system-wide instance.

gem_package resource has a property CALLED “gem_binary” property that is used by Chef Client to DETECT the environment settings and then install the gems.       "chef_gem" resource is having all properties and options as that of “gem_package” resource except the “gem_binary” property.”chef_gem” resource always USES “CurrentGemEnvironment” where the Chef Client is running.

“chef_gem” resource has additional functions of 

• Running its actions immediately before the convergence of the node. This allows the GEM to be used in the recipe just after it’s installation.
• Gems are made aware of the changes so that they could be used immediately by running “Gem.clear_paths”.