Diatreme Hajnáčka – hradný vrch contains a rare large feldspar megacrysts and syenitic xenoliths. X-ray diffraction reveal, that the studied feldspar megacrysts are structural high disordered albite and sanidines. In general, a homogenious megacrysts of feldspars and the high disorder of this feldspars indicates a high temperature origin and their relatively fast cooling. On the other hand, some of the albites contains a lamellae of Kfs. Syenite xenoliths composed of mineral association Pl–Kfs or Pl–Kfs–Qtz include also a idiomorph diopsid, plagioclase, magnetite, coroded amphibole and rhönite in silicic glass. In the one sample of syenite xenolith, the K-feldspar contain a celsian molecule (Ba content in Kfs 0,230 – 0,234 apfu). The final stage crystallization of rezidual melt is reprezented by barit. Results of feldspar (solvus) thermobarometry expose a crustal level P‒T (562 °C < T < 635 °C, P = 5 kbar) condtions of formation for syenite xenoliths, but on the other hand, the single pyroxen thermobarometry revealed inflow of fresh hot bazaltic melt (probably around 1200 °C). Syenite xenoliths thus represent a final stage differentiation of alkali basaltic melt in crustal level conditions. Origin of feldspar megacrysts might be similar to that syenite xenoliths, but the high structural disordered suggests a higher temperature formation and faster uprise of vulcanic material.