This 4 character Chinese proverb is most often used in circumstances where it is thought that saying nothing is preferable to speaking. It can also used to describe the meditative thoughts of a person, that emptiness in the mind, which is useful or 'golden'.
chénmò shì jīn
Silence is Golden
It is thought that the full quote is:
shuōhuà shì yín, chénmò shì jīn
Speaking is silver, Silence is golden
although the shorter version is much more commonly used.