Howling Stones

Enter another realm in the amazing world of the Humanx Commonwealth--the interstellar empire governed jointly by humans and aliens!
The newly discovered planet of Senisran was a veritable paradise--a sprawling world of vast oceans dotted with thousands of lush islands and copious deposits of rare-earths and minerals. First-contact specialist Pulickel Tomochelor's mission to Senisran was straightforward: Secure mining rights for the Humanx Commonwealth before the vicious AAnn Empire beat them to the chase. With Senisran's Parramat clan resisting entreaty, negotiations could be difficult, but Pulickel was more comfortable with aliens than with his own species, and looked forward to a triumphant return to Earth.
He hadn't counted on the incredible secret of Parramat, though: the strange, powerful green stones that the tribe used to manipulate the forces of nature. Within those stones lay an awesome technology the origin of which was lost in time--a technology that had to be kept from the AAnn at any cost . . . "From the Paperback edition."