Abstract: An apparatus to directly detect solids formation in a fluid under known pressure and temperature conditions is disclosed. The apparatus includes a vessel having an electromagnetic resonant cavity defined by an upper portion, a lower portion and a gap defined therebetween, the gap having resonant properties sensitive to the presence of a solid phase therein. The upper portion or the lower portion may be provided with a passage extending therethrough in fluid communication with an inlet to allow ingress of a stream of fluid to the gap and thereby purge solids from the cavity subsequent to solids formation. The apparatus also includes one or more probes, one or more sensors and a signal processor operatively connected to said sensors and said one or more probes to directly detect solids formation in the fluid within the cavity in response to detected changes in the resonant properties of the cavity.