What state of matter is spirit?

The spirit body—or the body in which the spirit dwells is more akin to a liquid or a gas than to any more solid material substance. 

It is a great white light that is vibrating at a rate of more than seven hundred and sixty-four trillion times per second, and is therefore not visible, except to clairvoyant vision—or to an eye attuned to a higher rate of vibration than that of which the physical eye is capable. 

The spirit body is composed of spiritual material, which compared to physical material is like the finest piece of silk compared to a piece of gunny sack or any other coarsely woven material.

The spirit body differs in the fineness of the particles of which it is composed in the quality of these particles, and in the workmanship and skill with which these particles have been woven together.

Fragments of Spiritual Knowledge Pertaining to the Spiritual World