During the Neolithic age what did workers discover inside of rocks when they heated them?

Workers heated rocks and discovered melted copper inside them. They then experimented with making the copper into tools and weapons. These proved to be easier to make and use than those made of stone. Craftspeople in western Asia discovered that mixing copper and tin formed bronze.

Explanation:

the minoan civilization flourished in the middle bronze age on the island of crete located in the eastern mediterranean from c. 2000 bce until c. 1500 bce. with their unique art and architecture, and the spread of their ideas through contact with other cultures across the aegean, the minoans made a significant contribution to the development of western european civilization as it is known today. labyrinth-like palace complexes, vivid frescoes depicting scenes such as bull-leaping and processions, fine gold jewelry, elegant stone vases, and pottery with vibrant decorations of marine life are all particular features of minoan crete.  

so basically their unique way of ding arts, as well as architecture.