I've never heard that, and considering the description of a liquid from my chem class, it does not fit it.

I'm pretty sure they are solid. You aren't thinking of glass, are you?

it is not, someone must be pulling your leg. Diamonds may be molten when they first form, but they are formed from solid carbon under extreme temperature and pressure.

You might have heard of the rare phenomenon where some crystals and diamonds have liquid trapped inside them. "One very revealing curiosity found contained within some Herkimer Diamonds are liquid inclusions. Many crystals have liquid trapped inside, but the high clarity of the Herkimer Diamond allows these inclusions to be seen with the naked eye. Study of liquid inclusions in Herkimer Diamonds sheds some light on the conditions which existed during their formation. Analysis of the liquid inside the inclusion shows that the solution is mostly water and salts. This salt water was trapped inside the diamonds during their growth stage, confirming that seawater was present. Many of these liquid inclusions have bubbles which float about in the liquid. Some of the bubbles are CO2 gas, but not all. In fact, most of the bubbles are water vapor. During the eighteen hundreds, an English geologist, Henry Clifton Sobry, theorized these bubbles could be a result of liquids being trapped at higher temperatures and then cooling. He proved his theory by gradually heating a crystal which held a bubble in a liquid in a liquid inclusion. As the liquid warmed, the bubble slowly disappeared." http://www.herkimerdiamond.com/History06.html