Wat Phra Kaew
The famous Emerald Buddha of Wat Phra Kaew is actually carved from a block of jade.
It was discovered in 1434 in a stupa in Chiang Raiu. It was covered with plaster at the time, so everyone thought it was an ordinary Buddha image. Later on, however, the abbot who found it noticed that the plaster on the nose had flaked off, revealing the green stone underneath. He assume the stone was emerald, and thus the legend of the Emerald Buddha was born.